Clamp Ironing Line Spacing to a Usable Minimum

An ironing line spacing of 0 reached the fillers from a 3MF, the CLI or
the per-filament override, which has no GUI guard. Concentric ironing
then never finished slicing, because a zero inset never shrinks the
region, and rectilinear ironing was silently dropped. Tiny positive
values produced an unprintable number of lines.

Top surface and support ironing now clamp the spacing to the 0.05 mm
floor the process GUI guard already enforces, so these configurations
iron at that spacing. Spacings at or above the floor, including every
shipped profile, are unchanged. The concentric filler also returns early
on a non-positive step so no other caller can hang it, and the filament
settings page now resets a too-small override the same way the process
page does.

src/libslic3r/Fill/Fill.cpp

@@ -1692,9 +1692,9 @@ void Layer::make_ironing()
 				ironing_params.just_infill 	= false;
 				// ORCA: Get filament-specific overrides if configured, otherwise use process values
 				size_t extruder_idx = ironing_params.extruder - 1;
-				ironing_params.line_spacing = (!config.filament_ironing_spacing.is_nil(extruder_idx)
+				ironing_params.line_spacing = std::max(IRONING_SPACING_MIN, !config.filament_ironing_spacing.is_nil(extruder_idx)
 					? config.filament_ironing_spacing.get_at(extruder_idx)
-					: config.ironing_spacing);
+					: config.ironing_spacing.value);
                 ironing_params.inset = (!config.filament_ironing_inset.is_nil(extruder_idx)
 					? config.filament_ironing_inset.get_at(extruder_idx)
 					: config.ironing_inset);

src/libslic3r/Fill/FillConcentric.cpp

@@ -22,6 +22,9 @@ void FillConcentric::_fill_surface_single(
     
     coord_t min_spacing = scale_(this->spacing) * params.multiline;
     coord_t distance = coord_t(min_spacing / params.density);
+    // A non-positive step never shrinks the region, so the inset loop below would not end.
+    if (min_spacing <= 0 || distance <= 0)
+        return;
     
     if (params.density > 0.9999f && !params.dont_adjust) {
         distance = this->_adjust_solid_spacing(bounding_box.size()(0), distance);
@@ -108,6 +111,8 @@ void FillConcentric::_fill_surface_single(const FillParams& params,
     // no rotation is supported for this infill pattern
     Point   bbox_size = expolygon.contour.bounding_box().size();
     coord_t min_spacing = scaled<coord_t>(this->spacing);
+    if (min_spacing <= 0)
+        return;
 
     if (params.density > 0.9999f && !params.dont_adjust) {
         coord_t                loops_count = std::max(bbox_size.x(), bbox_size.y()) / min_spacing + 1;

src/libslic3r/GCode.cpp

@@ -2504,7 +2504,8 @@ void GCode::do_export(Print* print, const char* path, GCodeProcessorResult* resu
 
     {
         LifecycleEventContext ctx;
-        ctx.name = std::to_string(print->model().id().id);
+        ctx.id = std::to_string(print->model().id().id);
+        ctx.name = print->get_model_name();
         ctx.code = LifecycleEvtCode::Ok;
         ctx.msg  = path;
         ctx.cancellation_check = [print]() { return print->canceled(); };
@@ -2556,7 +2557,8 @@ void GCode::do_export(Print* print, const char* path, GCodeProcessorResult* resu
         }
         {
             LifecycleEventContext ctx;
-            ctx.name = std::to_string(print->model().id().id);
+            ctx.id = std::to_string(print->model().id().id);
+            ctx.name = print->get_model_name();
             ctx.code = LifecycleEvtCode::Error;
             ctx.msg  = std::string(path) + "\n" + err_msg;
             ctx.cancellation_check = [print]() { return print->canceled(); };
@@ -2580,7 +2582,8 @@ void GCode::do_export(Print* print, const char* path, GCodeProcessorResult* resu
         boost::nowide::remove(path_tmp.c_str());
         {
             LifecycleEventContext ctx;
-            ctx.name = std::to_string(print->model().id().id);
+            ctx.id = std::to_string(print->model().id().id);
+            ctx.name = print->get_model_name();
             ctx.code = LifecycleEvtCode::Error;
             ctx.msg  = std::string(path) + "\n" + ex.what();
             ctx.cancellation_check = [print]() { return print->canceled(); };
@@ -2693,7 +2696,8 @@ void GCode::do_export(Print* print, const char* path, GCodeProcessorResult* resu
     if (ret) {
         {
             LifecycleEventContext ctx;
-            ctx.name = std::to_string(print->model().id().id);
+            ctx.id = std::to_string(print->model().id().id);
+            ctx.name = print->get_model_name();
             ctx.code = LifecycleEvtCode::Error;
             ctx.msg  = std::string(path) + "\nFailed to rename the output G-code file: " + ret.message();
             ctx.cancellation_check = [print]() { return print->canceled(); };
@@ -2712,7 +2716,8 @@ void GCode::do_export(Print* print, const char* path, GCodeProcessorResult* resu
 
     {
         LifecycleEventContext ctx;
-        ctx.name = std::to_string(print->model().id().id);
+        ctx.id = std::to_string(print->model().id().id);
+        ctx.name = print->get_model_name();
         ctx.code = LifecycleEvtCode::Ok;
         ctx.msg  = path;
         ctx.cancellation_check = [print]() { return print->canceled(); };

src/libslic3r/Print.cpp

@@ -2717,7 +2717,8 @@ void Print::process(long long *time_cost_with_cache, bool use_cache)
 
     {
         LifecycleEventContext ctx;
-        ctx.name = std::to_string(m_model.id().id);
+        ctx.id = std::to_string(m_model.id().id);
+        ctx.name = get_model_name();
         ctx.code = LifecycleEvtCode::Ok;
         ctx.cancellation_check = [this]() { return canceled(); };
         fire_lifecycle_event(LifecycleEvent::SliceStarted, ctx);
@@ -3344,7 +3345,8 @@ void Print::process(long long *time_cost_with_cache, bool use_cache)
 
     {
         LifecycleEventContext ctx;
-        ctx.name = std::to_string(m_model.id().id);
+        ctx.id = std::to_string(m_model.id().id);
+        ctx.name = get_model_name();
         ctx.code = LifecycleEvtCode::Ok;
         ctx.cancellation_check = [this]() { return canceled(); };
         fire_lifecycle_event(LifecycleEvent::SliceGeometryFinished, ctx);
@@ -4950,7 +4952,8 @@ void Print::export_gcode_from_previous_file(const std::string& file, GCodeProces
 {
     {
         LifecycleEventContext ctx;
-        ctx.name = std::to_string(m_model.id().id);
+        ctx.id = std::to_string(m_model.id().id);
+        ctx.name = get_model_name();
         ctx.code = LifecycleEvtCode::Ok;
         ctx.msg  = file;
         ctx.cancellation_check = [this]() { return canceled(); };
@@ -4980,7 +4983,8 @@ void Print::export_gcode_from_previous_file(const std::string& file, GCodeProces
         BOOST_LOG_TRIVIAL(error) << __FUNCTION__ <<  boost::format(": found errors when process gcode file %1%") %file.c_str();
         {
             LifecycleEventContext ctx;
-            ctx.name = std::to_string(m_model.id().id);
+            ctx.id = std::to_string(m_model.id().id);
+            ctx.name = get_model_name();
             ctx.code = LifecycleEvtCode::Error;
             ctx.msg  = file + "\n" + ex.what();
             ctx.cancellation_check = [this]() { return canceled(); };
@@ -4994,7 +4998,8 @@ void Print::export_gcode_from_previous_file(const std::string& file, GCodeProces
 
     {
         LifecycleEventContext ctx;
-        ctx.name = std::to_string(m_model.id().id);
+        ctx.id = std::to_string(m_model.id().id);
+        ctx.name = get_model_name();
         ctx.code = LifecycleEvtCode::Ok;
         ctx.msg  = file;
         ctx.cancellation_check = [this]() { return canceled(); };

src/libslic3r/PrintConfig.hpp

@@ -178,6 +178,10 @@ enum class IroningType {
     Count,
 };
 
+// Smallest usable ironing line spacing. Anything tighter yields an unprintable number of lines,
+// and zero stops the fillers from making progress.
+constexpr double IRONING_SPACING_MIN = 0.05;
+
 //BBS
 enum class WallInfillOrder {
     InnerOuterInfill,

src/libslic3r/Support/SupportParameters.hpp

@@ -64,7 +64,7 @@ struct SupportParameters {
 
         this->ironing = object_config.support_ironing;
         this->ironing_flow = support_material_interface_flow.with_height(support_material_interface_flow.height() * 0.01 * object_config.support_ironing_flow.value);
-        this->ironing_spacing = object_config.support_ironing_spacing;
+        this->ironing_spacing = std::max(IRONING_SPACING_MIN, object_config.support_ironing_spacing.value);
         this->ironing_pattern = object_config.support_ironing_pattern;
 
         // Calculate a minimum support layer height as a minimum over all extruders, but not smaller than 10um.

src/slic3r/GUI/ConfigManipulation.cpp

@@ -210,6 +210,30 @@ void ConfigManipulation::check_filament_max_volumetric_speed(DynamicPrintConfig
 
 }
 
+void ConfigManipulation::check_filament_ironing_spacing(DynamicPrintConfig *config)
+{
+    const auto *opt = config->option<ConfigOptionFloatsNullable>("filament_ironing_spacing");
+    if (opt == nullptr)
+        return;
+    std::vector<double> values = opt->values;
+    bool                reset  = false;
+    for (size_t i = 0; i < values.size(); ++i)
+        if (!opt->is_nil(i) && values[i] < IRONING_SPACING_MIN) {
+            values[i] = 0.1;
+            reset     = true;
+        }
+    if (!reset)
+        return;
+    const wxString     msg_text = _(L("Ironing spacing too small\nIt has been reset to 0.1"));
+    MessageDialog      dialog(nullptr, msg_text, "", wxICON_WARNING | wxOK);
+    DynamicPrintConfig new_conf = *config;
+    is_msg_dlg_already_exist    = true;
+    dialog.ShowModal();
+    new_conf.set_key_value("filament_ironing_spacing", new ConfigOptionFloatsNullable(values));
+    apply(config, &new_conf);
+    is_msg_dlg_already_exist = false;
+}
+
 void ConfigManipulation::check_chamber_temperature(DynamicPrintConfig* config)
 {
    bool support_chamber_temp_control=GUI::wxGetApp().preset_bundle->printers.get_selected_preset().config.opt_bool("support_chamber_temp_control");
@@ -332,7 +356,7 @@ void ConfigManipulation::update_print_fff_config(DynamicPrintConfig* config, con
     }
 
     //BBS: ironing_spacing shouldn't be too small or equal to zero
-    if (config->opt_float("ironing_spacing") < 0.05)
+    if (config->opt_float("ironing_spacing") < IRONING_SPACING_MIN)
     {
         const wxString msg_text = _(L("Ironing spacing too small\nIt has been reset to 0.1"));
         MessageDialog dialog(nullptr, msg_text, "", wxICON_WARNING | wxOK);
@@ -343,7 +367,7 @@ void ConfigManipulation::update_print_fff_config(DynamicPrintConfig* config, con
         apply(config, &new_conf);
         is_msg_dlg_already_exist = false;
     }
-    if (config->opt_float("support_ironing_spacing") < 0.05)
+    if (config->opt_float("support_ironing_spacing") < IRONING_SPACING_MIN)
     {
         const wxString msg_text = _(L("Ironing spacing too small\nIt has been reset to 0.1"));
         MessageDialog dialog(nullptr, msg_text, "", wxICON_WARNING | wxOK);

src/slic3r/GUI/ConfigManipulation.hpp

@@ -84,6 +84,7 @@ public:
     void    check_nozzle_temperature_initial_layer_range(DynamicPrintConfig* config);
     void    check_adaptive_pressure_advance_model(DynamicPrintConfig* config);
     void    check_filament_max_volumetric_speed(DynamicPrintConfig *config);
+    void    check_filament_ironing_spacing(DynamicPrintConfig *config);
     void    check_chamber_temperature(DynamicPrintConfig* config);
     void    check_chamber_minimal_temperature(DynamicPrintConfig* config);
     bool    check_layer_height(DynamicPrintConfig* config);

src/slic3r/GUI/Plater.cpp

@@ -12800,8 +12800,6 @@ void Plater::priv::on_process_completed(SlicingProcessCompletedEvent &evt)
     notification_manager->set_slicing_progress_export_possible();
 
     // Reset the "export G-code path" name, so that the automatic background processing will be enabled again.
-    const std::string lifecycle_job_name = this->background_process.fff_print() ?
-        this->background_process.fff_print()->output_filename() : std::string();
     this->background_process.reset_export();
     // This bool stops showing export finished notification even when process_completed_with_error is false
     bool has_error = false;
@@ -12848,8 +12846,18 @@ void Plater::priv::on_process_completed(SlicingProcessCompletedEvent &evt)
 
     {
         Slic3r::LifecycleEventContext ctx;
-        ctx.name = lifecycle_job_name;
+        if (const PrintBase* print = this->background_process.current_print()) {
-        ctx.code = evt.cancelled() ? Slic3r::LifecycleEvtCode::Warn : (has_error ? Slic3r::LifecycleEvtCode::Error : Slic3r::LifecycleEvtCode::Ok);
+            const Model& model = print->model();
+            ctx.id             = std::to_string(model.id().id);
+            if (model.model_info)
+                ctx.name = model.model_info->model_name;
+        } else {
+            // Realistically Printbase* print will never be null because select_technology already asserts an active print
+            // and the worker thread asserts it before processing.
+            BOOST_LOG_TRIVIAL(warning) << __FUNCTION__ << ": slicing completed without an active print; lifecycle event has no model ID";
+        }
+        ctx.code = evt.cancelled() ? Slic3r::LifecycleEvtCode::Warn :
+                                     (has_error ? Slic3r::LifecycleEvtCode::Error : Slic3r::LifecycleEvtCode::Ok);
         ctx.msg  = evt.cancelled() ? "cancelled" : (has_error ? lifecycle_error_msg : std::string());
         Slic3r::fire_lifecycle_event(Slic3r::LifecycleEvent::SlicingJobComplete, ctx);
     }

src/slic3r/GUI/Tab.cpp

@@ -4905,6 +4905,7 @@ void TabFilament::update()
         return; // ys_FIXME
 
     m_config_manipulation.check_filament_max_volumetric_speed(m_config);
+    m_config_manipulation.check_filament_ironing_spacing(m_config);
 
     m_update_cnt++;
 

src/slic3r/Utils/PrintHost.cpp

@@ -6,6 +6,7 @@
 #include <boost/optional.hpp>
 #include <boost/log/trivial.hpp>
 #include <boost/filesystem.hpp>
+#include <nlohmann/json.hpp>
 
 #include <wx/string.h>
 #include <wx/app.h>
@@ -115,10 +116,67 @@ std::string PrintHost::get_print_host_webui(DynamicPrintConfig* config)
     return webui_url;
 }
 
+namespace {
+
+// Moonraker (Klipper's API server) reports a raised exception as { "error": { "code", "message", "traceback" } }
+// under every host type that connects to it, often with the cause only in the traceback. Returns the reason to show,
+// or empty for any other body.
+std::string moonraker_error_reason(const std::string &body)
+{
+    const auto root = nlohmann::json::parse(body, nullptr, false);
+    const auto err  = root.find("error");
+    if (err == root.end())
+        return {};
+    const auto message   = err->find("message");
+    const auto traceback = err->find("traceback");
+    if (message == err->end() || traceback == err->end() || !message->is_string() || !traceback->is_string())
+        return {};
+
+    const auto &msg = message->get_ref<const std::string &>();
+    const auto &tb  = traceback->get_ref<const std::string &>();
+    if (msg.empty())
+        return {};
+    const auto end = tb.find_last_not_of(" \t\r\n");
+    if (end == std::string::npos)
+        return msg;
+
+    // Chained exceptions each start a new traceback; the one that failed the request is the last.
+    const auto header = tb.rfind("Traceback (most recent call last):", end);
+
+    // Tornado renders a raised HTTPError as "HTTP <code>: <reason>[ (<detail>)]", and the detail may span lines.
+    const auto code = err->find("code");
+    if (code != err->end() && code->is_number_integer()) {
+        const std::string marker = "HTTP " + std::to_string(code->get<int>()) + ": ";
+        const auto        pos    = tb.rfind(marker, end);
+        if (pos != std::string::npos && (header == std::string::npos || pos > header) && pos + marker.size() <= end) {
+            const std::string reason = tb.substr(pos + marker.size(), end + 1 - pos - marker.size());
+            // An HTTPError whose detail equals its reason, like HTTPError(401, "Unauthorized"), renders the phrase twice.
+            return reason == msg + " (" + msg + ")" ? msg : reason;
+        }
+    }
+
+    // Any other exception's type and message are everything from the first unindented line after its frames.
+    auto begin = (header == std::string::npos) ? std::string::npos : tb.find('\n', header);
+    while (begin != std::string::npos && begin < end) {
+        ++begin;
+        if (tb[begin] != ' ' && tb[begin] != '\r' && tb[begin] != '\n')
+            break;
+        begin = tb.find('\n', begin);
+    }
+    if (begin == std::string::npos || begin > end) {
+        const auto nl = tb.rfind('\n', end);
+        begin         = (nl == std::string::npos) ? 0 : nl + 1;
+    }
+    return msg + " (" + tb.substr(begin, end + 1 - begin) + ")";
+}
+
+} // namespace
+
 wxString PrintHost::format_error(const std::string &body, const std::string &error, unsigned status) const
 {
     if (status != 0) {
-        auto wxbody = wxString::FromUTF8(body.data());
+        const std::string reason = moonraker_error_reason(body);
+        auto wxbody = wxString::FromUTF8(reason.empty() ? body : reason);
         return wxString::Format("HTTP %u: %s", status, wxbody);
     } else {
         if (error.find("curl:Timeout was reached") != std::string::npos) {

tests/fff_print/test_fill.cpp

@@ -747,6 +747,61 @@ TEST_CASE("A region with ironing turned off is never ironed", "[Fill]")
     REQUIRE(Layer::choose_ironing_extruder(cfg, spiral_mode, /*is_topmost_layer=*/true) == -1);
 }
 
+// Ironing path count and total length in mm, over the whole object.
+static std::pair<size_t, double> ironing_extent(const Print &print)
+{
+    size_t paths  = 0;
+    double length = 0.;
+    for (const Layer *layer : print.objects().front()->layers())
+        for (const LayerRegion *region : layer->regions())
+            for (const ExtrusionEntity *entity : region->fills.flatten().entities)
+                if (ironing_role(entity->role())) {
+                    ++paths;
+                    length += unscale<double>(entity->length());
+                }
+    return {paths, length};
+}
+
+TEST_CASE("Ironing spacing below the minimum irons at the minimum spacing", "[Fill]")
+{
+    const std::string pattern      = GENERATE("rectilinear", "concentric");
+    const bool        via_filament = GENERATE(false, true);
+    const double      spacing      = GENERATE(0., 0.001);
+    CAPTURE(pattern, via_filament, spacing);
+
+    auto ironing_for = [&pattern, via_filament](double spacing) {
+        DynamicPrintConfig config = DynamicPrintConfig::full_print_config();
+        config.set_deserialize_strict({{"ironing_type", "top"},
+                                       {"ironing_pattern", pattern},
+                                       {"layer_height", 0.2}});
+        // The filament override replaces the process spacing, which stays at a usable value.
+        if (via_filament)
+            config.set_deserialize_strict({{"ironing_spacing", 0.1}, {"filament_ironing_spacing", spacing}});
+        else
+            config.set_deserialize_strict({{"ironing_spacing", spacing}});
+        Print print;
+        Slic3r::Test::init_and_process_print({Slic3r::Test::cube(20)}, print, config);
+        return ironing_extent(print);
+    };
+
+    const std::pair<size_t, double> clamped = ironing_for(spacing);
+    const std::pair<size_t, double> minimum = ironing_for(IRONING_SPACING_MIN);
+    REQUIRE(minimum.first > 0);
+    CHECK(clamped.first == minimum.first);
+    CHECK_THAT(clamped.second, Catch::Matchers::WithinRel(minimum.second, 1e-9));
+}
+
+TEST_CASE("Concentric fill at zero spacing returns without paths", "[Fill]")
+{
+    std::unique_ptr<Fill> filler(Fill::new_from_type(ipConcentric));
+    filler->spacing      = 0.;
+    filler->bounding_box = BoundingBox(Point(0, 0), Point::new_scale(10, 10));
+    FillParams params;
+    params.density = 1.f;
+    Surface surface(stTop, ExPolygon({Point(0, 0), Point::new_scale(10, 0), Point::new_scale(10, 10), Point::new_scale(0, 10)}));
+    CHECK(filler->fill_surface(&surface, params).empty());
+}
+
 TEST_CASE("Solid infill direction offsets every layer when no template is set", "[Fill]")
 {
     auto angles_for = [](int direction) {

tests/fff_print/test_print.cpp

@@ -15,6 +15,9 @@
 #include "libslic3r/Layer.hpp"
 #include "libslic3r/Model.hpp"
 #include "libslic3r/GCodeReader.hpp"
+#include "libslic3r/GCode/GCodeProcessor.hpp"
+#include "libslic3r/Exception.hpp"
+#include "libslic3r/LifecycleEvents.hpp"
 
 #include "test_helpers.hpp"
 #include "test_utils.hpp"
@@ -22,7 +25,10 @@
 #include <algorithm>
 #include <fstream>
 #include <iterator>
+#include <memory>
 #include <string_view>
+#include <utility>
+#include <vector>
 
 using namespace Slic3r;
 using namespace Slic3r::Test;
@@ -224,8 +230,88 @@ std::string resolved_output_name(Model& model, const std::string& format, const
     return print.output_filename(filename_base);
 }
 
+struct ScopedLifecycleHook
+{
+    explicit ScopedLifecycleHook(LifecycleHookFn hook) { set_lifecycle_hook_fn(std::move(hook)); }
+    ~ScopedLifecycleHook() { set_lifecycle_hook_fn(nullptr); }
+};
+
 } // namespace
 
+TEST_CASE("Slicing lifecycle events identify the model", "[Print][LifecycleEvents]")
+{
+    struct ObservedEvent {
+        LifecycleEvent event;
+        std::string id;
+        std::string name;
+    };
+    std::vector<ObservedEvent> events;
+    ScopedLifecycleHook hook([&](LifecycleEvent event, const LifecycleEventContext& ctx) {
+        events.push_back({ event, ctx.id, ctx.name });
+    });
+
+    Print print;
+    Model model;
+    ModelInfo info;
+    info.model_name = "Lifecycle test model";
+    model.model_info = std::make_shared<ModelInfo>(std::move(info));
+    init_print({cube(20)}, print, model);
+
+    print.process();
+    ScopedTemporaryFile temp(".gcode");
+    print.export_gcode(temp.string(), nullptr, nullptr);
+    GCodeProcessorResult result;
+    print.export_gcode_from_previous_file(temp.string(), &result);
+
+    const std::string expected_id = std::to_string(print.model().id().id);
+    const std::vector<LifecycleEvent> expected_events = {
+        LifecycleEvent::SliceStarted,
+        LifecycleEvent::SliceGeometryFinished,
+        LifecycleEvent::GCodeExportStarted,
+        LifecycleEvent::GCodeExportFinished,
+        LifecycleEvent::GCodeExportStarted,
+        LifecycleEvent::GCodeExportFinished,
+    };
+    REQUIRE(events.size() == expected_events.size());
+    for (size_t i = 0; i < expected_events.size(); ++i) {
+        CHECK(events[i].event == expected_events[i]);
+        CHECK(events[i].id == expected_id);
+        CHECK(events[i].name == "Lifecycle test model");
+    }
+}
+
+TEST_CASE("Slicing lifecycle event name is empty without model metadata", "[Print][LifecycleEvents]")
+{
+    std::string event_id;
+    std::string event_name = "unset";
+    ScopedLifecycleHook hook([&](LifecycleEvent event, const LifecycleEventContext& ctx) {
+        if (event == LifecycleEvent::SliceStarted) {
+            event_id = ctx.id;
+            event_name = ctx.name;
+        }
+    });
+
+    Print print;
+    Model model;
+    init_print({cube(20)}, print, model);
+    print.process();
+
+    CHECK(event_id == std::to_string(print.model().id().id));
+    CHECK(event_name.empty());
+}
+
+TEST_CASE("Output filenames with numeric statistics fail before slicing finishes", "[Print][Regression]")
+{
+    DynamicPrintConfig config = DynamicPrintConfig::full_print_config();
+    config.set_key_value("filename_format", new ConfigOptionString("{int(total_weight*10) / 10.0}"));
+
+    Print print;
+    Model model;
+    init_print({cube(20)}, print, model, config);
+
+    CHECK_THROWS_AS(print.output_filename(), PlaceholderParserError);
+}
+
 TEST_CASE("Print: {first_object_name} names the first printable object on the plate", "[Print]")
 {
     Model model;

tests/slic3rutils/CMakeLists.txt

@@ -18,6 +18,7 @@ add_executable(${_TEST_NAME}_tests
     test_plugin_install.cpp
     test_plugin_lifecycle.cpp
     test_plugin_printer_agent.cpp
+    test_printhost.cpp
     test_slicing_pipeline_bindings.cpp
     test_slicing_pipeline_config.cpp
     test_plugin_sort.cpp

tests/slic3rutils/test_printhost.cpp

@@ -0,0 +1,213 @@
+#include <catch2/catch_all.hpp>
+
+#include <nlohmann/json.hpp>
+
+#include "slic3r/Utils/PrintHost.hpp"
+
+using namespace Slic3r;
+
+namespace {
+
+class TestPrintHost : public PrintHost
+{
+public:
+    using PrintHost::format_error;
+
+    const char* get_name() const override { return "Test"; }
+    bool test(wxString&) const override { return true; }
+    wxString get_test_ok_msg() const override { return {}; }
+    wxString get_test_failed_msg(wxString&) const override { return {}; }
+    bool upload(PrintHostUpload, ProgressFn, ErrorFn, InfoFn) const override { return true; }
+    bool has_auto_discovery() const override { return false; }
+    bool can_test() const override { return false; }
+    PrintHostPostUploadActions get_post_upload_actions() const override { return {}; }
+    std::string get_host() const override { return {}; }
+};
+
+std::string format_error(const std::string& body, const std::string& error, unsigned status)
+{
+    return TestPrintHost().format_error(body, error, status).ToStdString();
+}
+
+std::string envelope(int code, const std::string& message, const std::string& traceback)
+{
+    return nlohmann::json{{"error", {{"code", code}, {"message", message}, {"traceback", traceback}}}}.dump();
+}
+
+std::string moonraker_error(int code, const std::string& message, const std::string& detail = {})
+{
+    std::string line = "tornado.web.HTTPError: HTTP " + std::to_string(code) + ": " + message;
+    if (!detail.empty())
+        line += " (" + detail + ")";
+    return envelope(code, message, "Traceback (most recent call last):\n  ...\n" + line + "\n");
+}
+
+// A real Moonraker body for uploading a file that is being printed.
+constexpr const char* k_busy_file_403 =
+    R"JSON({"error": {"code": 403, "message": "Forbidden", "traceback": "Traceback (most recent call last):\n\n  File \"/home/lava/moonraker/moonraker/components/file_manager/file_manager.py\", line 1017, in _finish_gcode_upload\n    can_start = self._handle_operation_check(check_path)\n                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n\nmoonraker.utils.exceptions.ServerError: File currently in use\n\nDuring handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n\n  File \"/home/lava/moonraker/moonraker/components/application.py\", line 1069, in post\n    raise tornado.web.HTTPError(\ntornado.web.HTTPError: HTTP 403: Forbidden (File is loaded, upload not permitted)\n"}})JSON";
+
+} // namespace
+
+TEST_CASE("A Klipper upload error shows its reason instead of a Python traceback", "[PrintHost][Regression]")
+{
+    const std::string msg = format_error(k_busy_file_403, "", 403);
+    INFO("actual: " << msg);
+
+    CHECK(msg == "HTTP 403: Forbidden (File is loaded, upload not permitted)");
+    CHECK_THAT(msg, !Catch::Matchers::ContainsSubstring("Traceback"));
+    CHECK_THAT(msg, !Catch::Matchers::ContainsSubstring("file_manager.py"));
+}
+
+TEST_CASE("The specific cause is recovered from a file endpoint's traceback", "[PrintHost]")
+{
+    SECTION("a plain detail")
+    {
+        const std::string body = moonraker_error(403, "Forbidden", "File is loaded, upload not permitted");
+        CHECK(format_error(body, "", 403) == "HTTP 403: Forbidden (File is loaded, upload not permitted)");
+    }
+
+    SECTION("a detail whose own parentheses nest (a filename)")
+    {
+        const std::string detail = "Directory does not exist (/home/pi/gcodes/plate (1).gcode)";
+        const std::string body   = moonraker_error(400, "Bad Request", detail);
+        CHECK(format_error(body, "", 400) == "HTTP 400: Bad Request (" + detail + ")");
+    }
+
+    SECTION("a detail that contains the reason phrase")
+    {
+        const std::string body = moonraker_error(403, "Forbidden", "Forbidden zone: access denied");
+        CHECK(format_error(body, "", 403) == "HTTP 403: Forbidden (Forbidden zone: access denied)");
+    }
+
+    SECTION("a detail that spans lines")
+    {
+        const std::string detail = "Move out of range\nX=250.000 Y=10.000";
+        const std::string body   = moonraker_error(400, "Bad Request", detail);
+        CHECK(format_error(body, "", 400) == "HTTP 400: Bad Request (" + detail + ")");
+    }
+
+    SECTION("a detail that only repeats the reason phrase is dropped")
+    {
+        const std::string body = moonraker_error(401, "Unauthorized", "Unauthorized");
+        CHECK(format_error(body, "", 401) == "HTTP 401: Unauthorized");
+    }
+}
+
+TEST_CASE("An unhandled exception shows its type and message", "[PrintHost]")
+{
+    const std::string frame = "Traceback (most recent call last):\n"
+                              "  File \"/home/pi/moonraker/moonraker/components/file_manager/file_manager.py\", line 1, in write\n"
+                              "    self._write(data)\n";
+
+    SECTION("a one-line message")
+    {
+        const std::string body = envelope(500, "Internal Server Error", frame + "OSError: [Errno 28] No space left on device\n");
+        CHECK(format_error(body, "", 500) == "HTTP 500: Internal Server Error (OSError: [Errno 28] No space left on device)");
+    }
+
+    SECTION("a message that spans lines")
+    {
+        const std::string body = envelope(500, "Internal Server Error", frame + "ServerError: Klippy request failed\n  see klippy.log\n");
+        CHECK(format_error(body, "", 500) == "HTTP 500: Internal Server Error (ServerError: Klippy request failed\n  see klippy.log)");
+    }
+
+    SECTION("raised while handling an HTTPError with the same code")
+    {
+        const std::string traceback = frame + "tornado.web.HTTPError: HTTP 500: Internal Server Error (Database locked)\n\n"
+                                              "During handling of the above exception, another exception occurred:\n\n" +
+                                      frame + "OSError: [Errno 5] Input/output error\n";
+        const std::string body      = envelope(500, "Internal Server Error", traceback);
+        CHECK(format_error(body, "", 500) == "HTTP 500: Internal Server Error (OSError: [Errno 5] Input/output error)");
+    }
+
+    SECTION("a traceback with no header")
+    {
+        const std::string body = envelope(500, "Internal Server Error", "OSError: [Errno 5] Input/output error");
+        CHECK(format_error(body, "", 500) == "HTTP 500: Internal Server Error (OSError: [Errno 5] Input/output error)");
+    }
+}
+
+TEST_CASE("A reason already complete in message is shown unchanged", "[PrintHost]")
+{
+    SECTION("message is the whole reason, no trailing detail")
+    {
+        const std::string body = moonraker_error(503, "Klippy is not ready");
+        CHECK(format_error(body, "", 503) == "HTTP 503: Klippy is not ready");
+    }
+
+    SECTION("a message that itself contains parentheses is not duplicated")
+    {
+        const std::string reason = "Requested blocks (0-5) are unavailable";
+        const std::string body   = moonraker_error(400, reason);
+        CHECK(format_error(body, "", 400) == "HTTP 400: " + reason);
+    }
+}
+
+TEST_CASE("A Moonraker error with no usable detail shows just the reason phrase", "[PrintHost]")
+{
+    struct Case
+    {
+        const char* name;
+        const char* body;
+        unsigned status;
+        const char* expected;
+    };
+
+    const auto c = GENERATE(
+        Case{"an empty traceback", R"JSON({"error": {"code": 500, "message": "Internal Server Error", "traceback": ""}})JSON", 500,
+             "HTTP 500: Internal Server Error"},
+        Case{"a traceback of only whitespace", R"JSON({"error": {"code": 500, "message": "Internal Server Error", "traceback": "\n \n"}})JSON",
+             500, "HTTP 500: Internal Server Error"});
+
+    DYNAMIC_SECTION(c.name) { CHECK(format_error(c.body, "", c.status) == c.expected); }
+}
+
+TEST_CASE("A percent sign in the reason is not a format specifier", "[PrintHost]")
+{
+    const std::string body = moonraker_error(507, "Insufficient Storage", "disk 100% full");
+    CHECK(format_error(body, "", 507) == "HTTP 507: Insufficient Storage (disk 100% full)");
+}
+
+TEST_CASE("Error bodies that are not a Moonraker envelope are left unchanged", "[PrintHost]")
+{
+    SECTION("OctoPrint's string-valued error member")
+    {
+        const std::string body = R"JSON({"error": "File not found"})JSON";
+        CHECK(format_error(body, "", 404) == "HTTP 404: " + body);
+    }
+
+    SECTION("PrusaLink's top-level message, not under error")
+    {
+        const std::string body = R"JSON({"title": "Conflict", "message": "Printer is printing"})JSON";
+        CHECK(format_error(body, "", 409) == "HTTP 409: " + body);
+    }
+
+    SECTION("a body that is not JSON")
+    {
+        const std::string html = "<html><head><title>502 Bad Gateway</title></head></html>";
+        CHECK(format_error(html, "", 502) == "HTTP 502: " + html);
+    }
+
+    SECTION("an error object with no traceback")
+    {
+        const std::string body = R"JSON({"error": {"code": 500, "message": "Internal Server Error"}})JSON";
+        CHECK(format_error(body, "", 500) == "HTTP 500: " + body);
+    }
+
+    SECTION("an error object whose traceback is null")
+    {
+        const std::string body = R"JSON({"error": {"code": 500, "message": "Internal Server Error", "traceback": null}})JSON";
+        CHECK(format_error(body, "", 500) == "HTTP 500: " + body);
+    }
+
+    SECTION("an envelope whose reason phrase is empty")
+    {
+        const std::string body = envelope(403, "", "Traceback (most recent call last):\nOSError: denied\n");
+        CHECK(format_error(body, "", 403) == "HTTP 403: " + body);
+    }
+
+    SECTION("a transport error with no HTTP status")
+    {
+        CHECK(format_error("", "curl:Could not connect", 0) == "curl:Could not connect");
+    }
+}