Calculate max_tokens value for anthropic requests based on available context using official token counting api

Signed-off-by: Christopher Petito <chrisjpetito@gmail.com>

Author: krissetto

pkg/model/provider/anthropic/beta_client.go

@@ -38,6 +38,16 @@ func (c *Client) createBetaStream(
 		}
 	}
 
+	sys := extractBetaSystemBlocks(messages)
+
+	if used, err := countAnthropicTokensBeta(ctx, client, anthropic.Model(c.ModelConfig.Model), converted, sys, allTools); err == nil {
+		configuredMaxTokens := maxTokens
+		maxTokens = clampMaxTokens(anthropicContextLimit(c.ModelConfig.Model), used, maxTokens)
+		if maxTokens < configuredMaxTokens {
+			slog.Warn("Anthropic Beta API max_tokens clamped to", "max_tokens", maxTokens)
+		}
+	}
+
 	params := anthropic.BetaMessageNewParams{
 		Model:     anthropic.Model(c.ModelConfig.Model),
 		MaxTokens: maxTokens,
@@ -47,7 +57,7 @@ func (c *Client) createBetaStream(
 	}
 
 	// Populate proper Anthropic system prompt from input messages
-	if sys := extractBetaSystemBlocks(messages); len(sys) > 0 {
+	if len(sys) > 0 {
 		params.System = sys
 	}
 
@@ -186,3 +196,42 @@ func contentArrayBeta(m map[string]any) []any {
 	}
 	return nil
 }
+
+// countAnthropicTokensBeta calls Anthropic's Count Tokens API for the provided Beta API payload
+// and returns the number of input tokens.
+func countAnthropicTokensBeta(
+	ctx context.Context,
+	client anthropic.Client,
+	model anthropic.Model,
+	messages []anthropic.BetaMessageParam,
+	system []anthropic.BetaTextBlockParam,
+	anthropicTools []anthropic.BetaToolUnionParam,
+) (int64, error) {
+	params := anthropic.BetaMessageCountTokensParams{
+		Model:    model,
+		Messages: messages,
+	}
+	if len(system) > 0 {
+		params.System = anthropic.BetaMessageCountTokensParamsSystemUnion{
+			OfBetaTextBlockArray: system,
+		}
+	}
+	if len(anthropicTools) > 0 {
+		// Convert BetaToolUnionParam to BetaMessageCountTokensParamsToolUnion
+		toolParams := make([]anthropic.BetaMessageCountTokensParamsToolUnion, len(anthropicTools))
+		for i, tool := range anthropicTools {
+			if tool.OfTool != nil {
+				toolParams[i] = anthropic.BetaMessageCountTokensParamsToolUnion{
+					OfTool: tool.OfTool,
+				}
+			}
+		}
+		params.Tools = toolParams
+	}
+
+	result, err := client.Beta.Messages.CountTokens(ctx, params)
+	if err != nil {
+		return 0, err
+	}
+	return result.InputTokens, nil
+}

pkg/model/provider/anthropic/beta_client_test.go

@@ -0,0 +1,305 @@
+package anthropic
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/anthropics/anthropic-sdk-go"
+	"github.com/anthropics/anthropic-sdk-go/option"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/docker/cagent/pkg/chat"
+)
+
+// TestCountAnthropicTokensBeta_Success tests successful token counting for beta API
+func TestCountAnthropicTokensBeta_Success(t *testing.T) {
+	// Setup mock server
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "/v1/messages/count_tokens", r.URL.Path)
+		assert.Equal(t, "application/json", r.Header.Get("content-type"))
+		assert.NotEmpty(t, r.Header.Get("x-api-key"))
+
+		// Verify request body contains expected fields
+		var payload map[string]any
+		err := json.NewDecoder(r.Body).Decode(&payload)
+		assert.NoError(t, err)
+		assert.Equal(t, "claude-3-5-sonnet-20241022", payload["model"])
+		assert.NotNil(t, payload["messages"])
+
+		// Return mock response
+		w.Header().Set("content-type", "application/json")
+		err = json.NewEncoder(w).Encode(map[string]int64{"input_tokens": 150})
+		assert.NoError(t, err)
+	}))
+	defer server.Close()
+
+	// Create test data
+	messages := []anthropic.BetaMessageParam{
+		{
+			Role: anthropic.BetaMessageParamRoleUser,
+			Content: []anthropic.BetaContentBlockParamUnion{
+				{OfText: &anthropic.BetaTextBlockParam{Text: "Hello"}},
+			},
+		},
+	}
+	system := []anthropic.BetaTextBlockParam{
+		{Text: "You are helpful"},
+	}
+
+	// Create client with test server URL
+	client := anthropic.NewClient(
+		option.WithAPIKey("test-key"),
+		option.WithBaseURL(server.URL),
+	)
+
+	// Call function
+	tokens, err := countAnthropicTokensBeta(t.Context(), client, "claude-3-5-sonnet-20241022", messages, system, nil)
+
+	// Verify
+	require.NoError(t, err)
+	assert.Equal(t, int64(150), tokens)
+}
+
+// TestCountAnthropicTokensBeta_NoAPIKey tests error when API key is missing
+func TestCountAnthropicTokensBeta_NoAPIKey(t *testing.T) {
+	messages := []anthropic.BetaMessageParam{}
+	system := []anthropic.BetaTextBlockParam{}
+
+	// Create client without base URL to trigger error
+	client := anthropic.NewClient(
+		option.WithAPIKey("test-key"),
+		// No base URL set
+	)
+
+	tokens, err := countAnthropicTokensBeta(t.Context(), client, "claude-3-5-sonnet-20241022", messages, system, nil)
+
+	require.Error(t, err)
+	assert.Equal(t, int64(0), tokens)
+}
+
+// TestCountAnthropicTokensBeta_ServerError tests error handling for server errors
+func TestCountAnthropicTokensBeta_ServerError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer server.Close()
+
+	messages := []anthropic.BetaMessageParam{}
+	system := []anthropic.BetaTextBlockParam{}
+
+	// Create client with test server URL
+	client := anthropic.NewClient(
+		option.WithAPIKey("test-key"),
+		option.WithBaseURL(server.URL),
+	)
+
+	tokens, err := countAnthropicTokensBeta(t.Context(), client, "claude-3-5-sonnet-20241022", messages, system, nil)
+	require.Error(t, err)
+	assert.Equal(t, int64(0), tokens)
+}
+
+// TestCountAnthropicTokensBeta_WithTools tests token counting includes tools
+func TestCountAnthropicTokensBeta_WithTools(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var payload map[string]any
+		err := json.NewDecoder(r.Body).Decode(&payload)
+		assert.NoError(t, err)
+
+		// Verify tools are included in payload
+		assert.NotNil(t, payload["tools"])
+		tools, ok := payload["tools"].([]any)
+		assert.True(t, ok)
+		assert.Len(t, tools, 1)
+
+		w.Header().Set("content-type", "application/json")
+		err = json.NewEncoder(w).Encode(map[string]int64{"input_tokens": 200})
+		assert.NoError(t, err)
+	}))
+	defer server.Close()
+
+	messages := []anthropic.BetaMessageParam{}
+	system := []anthropic.BetaTextBlockParam{}
+	tools := []anthropic.BetaToolUnionParam{
+		{OfTool: &anthropic.BetaToolParam{
+			Name:        "test_tool",
+			Description: anthropic.String("A test tool"),
+		}},
+	}
+
+	// Create client with test server URL
+	client := anthropic.NewClient(
+		option.WithAPIKey("test-key"),
+		option.WithBaseURL(server.URL),
+	)
+
+	tokens, err := countAnthropicTokensBeta(t.Context(), client, "claude-3-5-sonnet-20241022", messages, system, tools)
+
+	require.NoError(t, err)
+	assert.Equal(t, int64(200), tokens)
+}
+
+// TestClampMaxTokens_WithinLimit tests clamping when configured tokens are within limit
+func TestClampMaxTokens_WithinLimit(t *testing.T) {
+	// Context limit: 200k, used: 50k, safety: 1k, remaining: 149k
+	// Configured: 8k (within limit)
+	result := clampMaxTokens(200000, 50000, 8000)
+	assert.Equal(t, int64(8000), result)
+}
+
+// TestClampMaxTokens_ExceedsLimit tests clamping when configured tokens exceed remaining
+func TestClampMaxTokens_ExceedsLimit(t *testing.T) {
+	// Context limit: 200k, used: 190k, safety: 1024, remaining: 8976
+	// Configured: 16k (exceeds limit)
+	result := clampMaxTokens(200000, 190000, 16000)
+	assert.Equal(t, int64(8976), result)
+}
+
+// TestClampMaxTokens_MinimumOne tests clamping never returns less than 1
+func TestClampMaxTokens_MinimumOne(t *testing.T) {
+	// Context limit: 200k, used: 199k, safety: 1k, remaining: 0 (would be negative)
+	result := clampMaxTokens(200000, 199000, 8000)
+	assert.Equal(t, int64(1), result)
+}
+
+// TestClampMaxTokens_ExactlyAtLimit tests clamping when used + safety equals limit
+func TestClampMaxTokens_ExactlyAtLimit(t *testing.T) {
+	// Context limit: 200k, used: 199k, safety: 1k, remaining: 0
+	result := clampMaxTokens(200000, 199000, 1000)
+	assert.Equal(t, int64(1), result)
+}
+
+// TestAnthropicContextLimit_ReturnsCorrectLimit tests context limit function
+func TestAnthropicContextLimit_ReturnsCorrectLimit(t *testing.T) {
+	limit := anthropicContextLimit("claude-3-5-sonnet-20241022")
+	assert.Equal(t, int64(200000), limit)
+}
+
+// TestExtractBetaSystemBlocks_SingleSystemMessage tests extracting system messages
+func TestExtractBetaSystemBlocks_SingleSystemMessage(t *testing.T) {
+	msgs := []chat.Message{
+		{
+			Role:    chat.MessageRoleSystem,
+			Content: "You are a helpful assistant",
+		},
+	}
+
+	blocks := extractBetaSystemBlocks(msgs)
+
+	require.Len(t, blocks, 1)
+	assert.Equal(t, "You are a helpful assistant", blocks[0].Text)
+}
+
+// TestExtractBetaSystemBlocks_MultipleSystemMessages tests extracting multiple system messages
+func TestExtractBetaSystemBlocks_MultipleSystemMessages(t *testing.T) {
+	msgs := []chat.Message{
+		{
+			Role:    chat.MessageRoleSystem,
+			Content: "You are helpful",
+		},
+		{
+			Role:    chat.MessageRoleUser,
+			Content: "Hello",
+		},
+		{
+			Role:    chat.MessageRoleSystem,
+			Content: "Be concise",
+		},
+	}
+
+	blocks := extractBetaSystemBlocks(msgs)
+
+	require.Len(t, blocks, 2)
+	assert.Equal(t, "You are helpful", blocks[0].Text)
+	assert.Equal(t, "Be concise", blocks[1].Text)
+}
+
+// TestExtractBetaSystemBlocks_SkipsEmptyText tests that empty system text is skipped
+func TestExtractBetaSystemBlocks_SkipsEmptyText(t *testing.T) {
+	msgs := []chat.Message{
+		{
+			Role:    chat.MessageRoleSystem,
+			Content: "   \n\t  ",
+		},
+		{
+			Role:    chat.MessageRoleSystem,
+			Content: "Valid system prompt",
+		},
+	}
+
+	blocks := extractBetaSystemBlocks(msgs)
+
+	require.Len(t, blocks, 1)
+	assert.Equal(t, "Valid system prompt", blocks[0].Text)
+}
+
+// TestExtractBetaSystemBlocks_MultiContent tests extracting from multi-content system messages
+func TestExtractBetaSystemBlocks_MultiContent(t *testing.T) {
+	msgs := []chat.Message{
+		{
+			Role: chat.MessageRoleSystem,
+			MultiContent: []chat.MessagePart{
+				{Type: chat.MessagePartTypeText, Text: "Part 1"},
+				{Type: chat.MessagePartTypeText, Text: "Part 2"},
+			},
+		},
+	}
+
+	blocks := extractBetaSystemBlocks(msgs)
+
+	require.Len(t, blocks, 2)
+	assert.Equal(t, "Part 1", blocks[0].Text)
+	assert.Equal(t, "Part 2", blocks[1].Text)
+}
+
+// TestConvertBetaMessages_UserMessage tests converting user messages
+func TestConvertBetaMessages_UserMessage(t *testing.T) {
+	msgs := []chat.Message{
+		{
+			Role:    chat.MessageRoleUser,
+			Content: "Hello, assistant!",
+		},
+	}
+
+	converted := convertBetaMessages(msgs)
+
+	require.Len(t, converted, 1)
+	assert.Equal(t, anthropic.BetaMessageParamRoleUser, converted[0].Role)
+	require.Len(t, converted[0].Content, 1)
+}
+
+// TestConvertBetaMessages_SkipsSystemMessages tests that system messages are skipped
+func TestConvertBetaMessages_SkipsSystemMessages(t *testing.T) {
+	msgs := []chat.Message{
+		{
+			Role:    chat.MessageRoleSystem,
+			Content: "System prompt",
+		},
+		{
+			Role:    chat.MessageRoleUser,
+			Content: "User message",
+		},
+	}
+
+	converted := convertBetaMessages(msgs)
+
+	require.Len(t, converted, 1)
+	assert.Equal(t, anthropic.BetaMessageParamRoleUser, converted[0].Role)
+}
+
+// TestConvertBetaMessages_AssistantMessage tests converting assistant messages
+func TestConvertBetaMessages_AssistantMessage(t *testing.T) {
+	msgs := []chat.Message{
+		{
+			Role:    chat.MessageRoleAssistant,
+			Content: "I can help with that",
+		},
+	}
+
+	converted := convertBetaMessages(msgs)
+
+	require.Len(t, converted, 1)
+	assert.Equal(t, anthropic.BetaMessageParamRoleAssistant, converted[0].Role)
+}