WI-001: #15 No exported setter for the package-level ProblemConfig

README.md

@@ -289,6 +289,20 @@ req, err := httpsuite.ParseRequest[*CreateUserRequest](
 )
 ```
 
+### Problem type URLs
+
+Set the base URL and extra error type paths once at startup; `GetProblemTypeURL` and the problem helpers pick them up. `ParseOptions.Problems` still overrides per call.
+
+```go
+cfg := httpsuite.NewProblemConfig()
+cfg.BaseURL = "https://api.example.com"
+cfg.ErrorTypePaths["unauthorized"] = "/errors/unauthorized"
+httpsuite.SetProblemConfig(cfg)
+
+// restore the built-in default
+httpsuite.SetProblemConfig(httpsuite.NewProblemConfig())
+```
+
 ## Direct helpers
 
 ```go

problem_config.go

@@ -1,8 +1,14 @@
 package httpsuite
 
-import "strings"
+import (
+	"strings"
+	"sync"
+)
 
-var defaultProblemConfig = NewProblemConfig()
+var (
+	defaultProblemConfigMu sync.RWMutex
+	defaultProblemConfig   = NewProblemConfig()
+)
 
 // ProblemConfig controls how problem type URLs are generated.
 type ProblemConfig struct {
@@ -24,9 +30,25 @@ func NewProblemConfig() ProblemConfig {
 
 // DefaultProblemConfig returns a copy of the package default config.
 func DefaultProblemConfig() ProblemConfig {
+	defaultProblemConfigMu.RLock()
+	defer defaultProblemConfigMu.RUnlock()
 	return defaultProblemConfig.Clone()
 }
 
+// SetProblemConfig replaces the package-level default config used by
+// GetProblemTypeURL, DefaultProblemConfig and the helpers that resolve problem
+// types. The config is copied, so later changes to cfg do not affect the
+// default. A per-call ParseOptions.Problems still overrides it.
+//
+// Call it once at startup. To restore the built-in default, call
+// SetProblemConfig(NewProblemConfig()).
+func SetProblemConfig(cfg ProblemConfig) {
+	clone := cfg.Clone()
+	defaultProblemConfigMu.Lock()
+	defer defaultProblemConfigMu.Unlock()
+	defaultProblemConfig = clone
+}
+
 func mergeProblemConfig(config *ProblemConfig) ProblemConfig {
 	merged := DefaultProblemConfig()
 	if config == nil {
@@ -71,6 +93,8 @@ func (c ProblemConfig) TypeURL(errorType string) string {
 
 // GetProblemTypeURL returns the default problem type URL for a known error type.
 func GetProblemTypeURL(errorType string) string {
+	defaultProblemConfigMu.RLock()
+	defer defaultProblemConfigMu.RUnlock()
 	return defaultProblemConfig.TypeURL(errorType)
 }
 

problem_config_test.go

@@ -1,6 +1,96 @@
 package httpsuite
 
-import "testing"
+import (
+	"sync"
+	"testing"
+)
+
+func restoreProblemConfig(t *testing.T) {
+	t.Helper()
+	SetProblemConfig(NewProblemConfig())
+	t.Cleanup(func() { SetProblemConfig(NewProblemConfig()) })
+}
+
+func TestSetProblemConfig(t *testing.T) {
+	restoreProblemConfig(t)
+
+	cfg := NewProblemConfig()
+	cfg.BaseURL = "https://api.example.com/"
+	cfg.ErrorTypePaths["unauthorized"] = "errors/unauthorized"
+	SetProblemConfig(cfg)
+
+	if got, want := GetProblemTypeURL("unauthorized"), "https://api.example.com/errors/unauthorized"; got != want {
+		t.Fatalf("expected %q, got %q", want, got)
+	}
+	if got := DefaultProblemConfig().TypeURL("not_found_error"); got != "https://api.example.com/errors/not-found" {
+		t.Fatalf("unexpected default type URL %q", got)
+	}
+	if got := NewBadRequestProblem("x").Type; got != "https://api.example.com/errors/bad-request" {
+		t.Fatalf("helper did not use configured default, got %q", got)
+	}
+}
+
+func TestSetProblemConfigCopiesInput(t *testing.T) {
+	restoreProblemConfig(t)
+
+	cfg := NewProblemConfig()
+	SetProblemConfig(cfg)
+	cfg.ErrorTypePaths["validation_error"] = "/mutated"
+
+	if got := GetProblemTypeURL("validation_error"); got != "/errors/validation-error" {
+		t.Fatalf("expected default to be isolated from caller map, got %q", got)
+	}
+}
+
+func TestParseOptionsProblemsOverrideSetProblemConfig(t *testing.T) {
+	restoreProblemConfig(t)
+
+	cfg := NewProblemConfig()
+	cfg.BaseURL = "https://global.example.com"
+	SetProblemConfig(cfg)
+
+	merged := mergeProblemConfig(&ProblemConfig{BaseURL: "https://local.example.com"})
+	if got, want := merged.TypeURL("validation_error"), "https://local.example.com/errors/validation-error"; got != want {
+		t.Fatalf("expected %q, got %q", want, got)
+	}
+	merged = mergeProblemConfig(nil)
+	if got, want := merged.TypeURL("validation_error"), "https://global.example.com/errors/validation-error"; got != want {
+		t.Fatalf("expected %q, got %q", want, got)
+	}
+}
+
+func TestSetProblemConfigRestore(t *testing.T) {
+	restoreProblemConfig(t)
+
+	SetProblemConfig(ProblemConfig{BaseURL: "https://api.example.com"})
+	if got := GetProblemTypeURL("validation_error"); got != BlankURL {
+		t.Fatalf("expected %q, got %q", BlankURL, got)
+	}
+
+	SetProblemConfig(NewProblemConfig())
+	if got := GetProblemTypeURL("validation_error"); got != "/errors/validation-error" {
+		t.Fatalf("expected built-in default, got %q", got)
+	}
+}
+
+func TestSetProblemConfigConcurrent(t *testing.T) {
+	restoreProblemConfig(t)
+
+	var wg sync.WaitGroup
+	for i := 0; i < 8; i++ {
+		wg.Add(2)
+		go func() {
+			defer wg.Done()
+			SetProblemConfig(NewProblemConfig())
+		}()
+		go func() {
+			defer wg.Done()
+			_ = GetProblemTypeURL("validation_error")
+			_ = DefaultProblemConfig()
+		}()
+	}
+	wg.Wait()
+}
 
 func TestProblemConfigTypeURL(t *testing.T) {
 	t.Parallel()