chore: correct last user prompt detection

anthropic.go

@@ -3,7 +3,6 @@ package aibridge
 import (
 	"encoding/json"
 	"errors"
-	"strings"
 
 	"github.com/anthropics/anthropic-sdk-go"
 	"github.com/anthropics/anthropic-sdk-go/packages/param"
@@ -51,22 +50,23 @@ func (b *MessageNewParamsWrapper) LastUserPrompt() (*string, error) {
 		return nil, errors.New("no messages")
 	}
 
-	var userMessage string
-	for i := len(b.Messages) - 1; i >= 0; i-- {
-		m := b.Messages[i]
-		if m.Role != anthropic.MessageParamRoleUser {
-			continue
-		}
-		if len(m.Content) == 0 {
-			continue
-		}
+	// We only care if the last message was issued by a user.
+	msg := b.Messages[len(b.Messages)-1]
+	if msg.Role != anthropic.MessageParamRoleUser {
+		return nil, nil
+	}
 
-		for j := len(m.Content) - 1; j >= 0; j-- {
-			if textContent := m.Content[j].GetText(); textContent != nil {
-				userMessage = *textContent
-			}
+	if len(msg.Content) == 0 {
+		return nil, nil
+	}
 
-			return utils.PtrTo(strings.TrimSpace(userMessage)), nil
+	// Walk backwards on "user"-initiated message content. Clients often inject
+	// content ahead of the actual prompt to provide context to the model,
+	// so the last item in the slice is most likely the user's prompt.
+	for i := len(msg.Content) - 1; i >= 0; i-- {
+		// Only text content is supported currently.
+		if textContent := msg.Content[i].GetText(); textContent != nil {
+			return textContent, nil
 		}
 	}
 

anthropic_test.go

@@ -0,0 +1,172 @@
+package aibridge_test
+
+import (
+	"testing"
+
+	"github.com/anthropics/anthropic-sdk-go"
+	"github.com/coder/aibridge"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAnthropicLastUserPrompt(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name        string
+		wrapper     *aibridge.MessageNewParamsWrapper
+		expected    string
+		expectError bool
+		errorMsg    string
+	}{
+		{
+			name:        "nil struct",
+			expectError: true,
+			errorMsg:    "nil struct",
+		},
+		{
+			name: "no messages",
+			wrapper: &aibridge.MessageNewParamsWrapper{
+				MessageNewParams: anthropic.MessageNewParams{
+					Messages: []anthropic.MessageParam{},
+				},
+			},
+			expectError: true,
+			errorMsg:    "no messages",
+		},
+		{
+			name: "last message not from user",
+			wrapper: &aibridge.MessageNewParamsWrapper{
+				MessageNewParams: anthropic.MessageNewParams{
+					Messages: []anthropic.MessageParam{
+						{
+							Role: anthropic.MessageParamRoleUser,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewTextBlock("user message"),
+							},
+						},
+						{
+							Role: anthropic.MessageParamRoleAssistant,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewTextBlock("assistant message"),
+							},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "last user message with empty content",
+			wrapper: &aibridge.MessageNewParamsWrapper{
+				MessageNewParams: anthropic.MessageNewParams{
+					Messages: []anthropic.MessageParam{
+						{
+							Role:    anthropic.MessageParamRoleUser,
+							Content: []anthropic.ContentBlockParamUnion{},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "last user message with single text content",
+			wrapper: &aibridge.MessageNewParamsWrapper{
+				MessageNewParams: anthropic.MessageNewParams{
+					Messages: []anthropic.MessageParam{
+						{
+							Role: anthropic.MessageParamRoleUser,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewTextBlock("Hello, world!"),
+							},
+						},
+					},
+				},
+			},
+			expected: "Hello, world!",
+		},
+		{
+			name: "last user message with multiple content blocks - text at end",
+			wrapper: &aibridge.MessageNewParamsWrapper{
+				MessageNewParams: anthropic.MessageNewParams{
+					Messages: []anthropic.MessageParam{
+						{
+							Role: anthropic.MessageParamRoleUser,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewImageBlockBase64("image/png", "base64data"),
+								anthropic.NewTextBlock("First text"),
+								anthropic.NewImageBlockBase64("image/jpeg", "moredata"),
+								anthropic.NewTextBlock("Last text"),
+							},
+						},
+					},
+				},
+			},
+			expected: "Last text",
+		},
+		{
+			name: "last user message with only non-text content",
+			wrapper: &aibridge.MessageNewParamsWrapper{
+				MessageNewParams: anthropic.MessageNewParams{
+					Messages: []anthropic.MessageParam{
+						{
+							Role: anthropic.MessageParamRoleUser,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewImageBlockBase64("image/png", "base64data"),
+								anthropic.NewImageBlockBase64("image/jpeg", "moredata"),
+							},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "multiple messages with last being user",
+			wrapper: &aibridge.MessageNewParamsWrapper{
+				MessageNewParams: anthropic.MessageNewParams{
+					Messages: []anthropic.MessageParam{
+						{
+							Role: anthropic.MessageParamRoleUser,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewTextBlock("First user message"),
+							},
+						},
+						{
+							Role: anthropic.MessageParamRoleAssistant,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewTextBlock("Assistant response"),
+							},
+						},
+						{
+							Role: anthropic.MessageParamRoleUser,
+							Content: []anthropic.ContentBlockParamUnion{
+								anthropic.NewTextBlock("Second user message"),
+							},
+						},
+					},
+				},
+			},
+			expected: "Second user message",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := tt.wrapper.LastUserPrompt()
+
+			if tt.expectError {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), tt.errorMsg)
+				require.Nil(t, result)
+			} else {
+				require.NoError(t, err)
+				// Check pointer equality - both nil or both non-nil
+				if tt.expected == "" {
+					require.Nil(t, result)
+				} else {
+					require.NotNil(t, result)
+					// The result should point to the same string from the content block
+					require.Equal(t, tt.expected, *result)
+				}
+			}
+		})
+	}
+}

bridge_integration_test.go

@@ -426,7 +426,7 @@ func TestSimple(t *testing.T) {
 
 					// Then: I expect the prompt to have been tracked.
 					require.NotEmpty(t, recorderClient.userPrompts, "no prompts tracked")
-					assert.Equal(t, "how many angels can dance on the head of a pin", recorderClient.userPrompts[0].Prompt)
+					assert.Contains(t, recorderClient.userPrompts[0].Prompt, "how many angels can dance on the head of a pin")
 
 					// Validate that responses have their IDs overridden with a interception ID rather than the original ID from the upstream provider.
 					// The reason for this is that Bridge may make multiple upstream requests (i.e. to invoke injected tools), and clients will not be expecting

openai.go

@@ -3,7 +3,6 @@ package aibridge
 import (
 	"encoding/json"
 	"errors"
-	"strings"
 
 	"github.com/anthropics/anthropic-sdk-go/shared"
 	"github.com/anthropics/anthropic-sdk-go/shared/constant"
@@ -56,22 +55,27 @@ func (c *ChatCompletionNewParamsWrapper) LastUserPrompt() (*string, error) {
 		return nil, errors.New("no messages")
 	}
 
-	var msg *openai.ChatCompletionUserMessageParam
-	for i := len(c.Messages) - 1; i >= 0; i-- {
-		m := c.Messages[i]
-		if m.OfUser != nil {
-			msg = m.OfUser
-			break
-		}
+	// We only care if the last message was issued by a user.
+	msg := c.Messages[len(c.Messages)-1]
+	if msg.OfUser == nil {
+		return nil, nil
 	}
 
-	if msg == nil {
-		return nil, nil
+	if msg.OfUser.Content.OfString.String() != "" {
+		return utils.PtrTo(msg.OfUser.Content.OfString.String()), nil
+	}
+
+	// Walk backwards on "user"-initiated message content. Clients often inject
+	// content ahead of the actual prompt to provide context to the model,
+	// so the last item in the slice is most likely the user's prompt.
+	for i := len(msg.OfUser.Content.OfArrayOfContentParts) - 1; i >= 0; i-- {
+		// Only text content is supported currently.
+		if textContent := msg.OfUser.Content.OfArrayOfContentParts[i].OfText; textContent != nil {
+			return &textContent.Text, nil
+		}
 	}
 
-	return utils.PtrTo(strings.TrimSpace(
-		msg.Content.OfString.String(),
-	)), nil
+	return nil, nil
 }
 
 func sumUsage(ref, in openai.CompletionUsage) openai.CompletionUsage {