feat: Add Anthropic Messages API support (#7948)

* Initial plan

* Add Anthropic Messages API support

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Fix code review comments: add error handling for JSON operations

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Fix test suite to use existing schema test runner

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Add Anthropic e2e tests using anthropic-sdk-go for streaming and non-streaming

Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

* Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: mudler <2420543+mudler@users.noreply.github.com>

tests/e2e/e2e_anthropic_test.go

@@ -0,0 +1,150 @@
+package e2e_test
+
+import (
+	"context"
+
+	"github.com/anthropics/anthropic-sdk-go"
+	"github.com/anthropics/anthropic-sdk-go/option"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Anthropic API E2E test", func() {
+	var client anthropic.Client
+
+	Context("API with Anthropic SDK", func() {
+		BeforeEach(func() {
+			// Create Anthropic client pointing to LocalAI
+			client = anthropic.NewClient(
+				option.WithBaseURL(localAIURL),
+				option.WithAPIKey("test-api-key"), // LocalAI doesn't require a real API key
+			)
+
+			// Wait for API to be ready by attempting a simple request
+			Eventually(func() error {
+				_, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
+					Model:     "gpt-4",
+					MaxTokens: 10,
+					Messages: []anthropic.MessageParam{
+						anthropic.NewUserMessage(anthropic.NewTextBlock("Hi")),
+					},
+				})
+				return err
+			}, "2m").ShouldNot(HaveOccurred())
+		})
+
+		Context("Non-streaming responses", func() {
+			It("generates a response for a simple message", func() {
+				message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
+					Model:     "gpt-4",
+					MaxTokens: 1024,
+					Messages: []anthropic.MessageParam{
+						anthropic.NewUserMessage(anthropic.NewTextBlock("How much is 2+2? Reply with just the number.")),
+					},
+				})
+				Expect(err).ToNot(HaveOccurred())
+				Expect(message.Content).ToNot(BeEmpty())
+				// Role is a constant type that defaults to "assistant"
+				Expect(string(message.Role)).To(Equal("assistant"))
+				Expect(message.StopReason).To(Equal(anthropic.MessageStopReasonEndTurn))
+				Expect(string(message.Type)).To(Equal("message"))
+
+				// Check that content contains text block with expected answer
+				Expect(len(message.Content)).To(BeNumerically(">=", 1))
+				textBlock := message.Content[0]
+				Expect(string(textBlock.Type)).To(Equal("text"))
+				Expect(textBlock.Text).To(Or(ContainSubstring("4"), ContainSubstring("four")))
+			})
+
+			It("handles system prompts", func() {
+				message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
+					Model:     "gpt-4",
+					MaxTokens: 1024,
+					System: []anthropic.TextBlockParam{
+						{Text: "You are a helpful assistant. Always respond in uppercase letters."},
+					},
+					Messages: []anthropic.MessageParam{
+						anthropic.NewUserMessage(anthropic.NewTextBlock("Say hello")),
+					},
+				})
+				Expect(err).ToNot(HaveOccurred())
+				Expect(message.Content).ToNot(BeEmpty())
+				Expect(len(message.Content)).To(BeNumerically(">=", 1))
+			})
+
+			It("returns usage information", func() {
+				message, err := client.Messages.New(context.TODO(), anthropic.MessageNewParams{
+					Model:     "gpt-4",
+					MaxTokens: 100,
+					Messages: []anthropic.MessageParam{
+						anthropic.NewUserMessage(anthropic.NewTextBlock("Hello")),
+					},
+				})
+				Expect(err).ToNot(HaveOccurred())
+				Expect(message.Usage.InputTokens).To(BeNumerically(">", 0))
+				Expect(message.Usage.OutputTokens).To(BeNumerically(">", 0))
+			})
+		})
+
+		Context("Streaming responses", func() {
+			It("streams tokens for a simple message", func() {
+				stream := client.Messages.NewStreaming(context.TODO(), anthropic.MessageNewParams{
+					Model:     "gpt-4",
+					MaxTokens: 1024,
+					Messages: []anthropic.MessageParam{
+						anthropic.NewUserMessage(anthropic.NewTextBlock("Count from 1 to 5")),
+					},
+				})
+
+				message := anthropic.Message{}
+				eventCount := 0
+				hasContentDelta := false
+
+				for stream.Next() {
+					event := stream.Current()
+					err := message.Accumulate(event)
+					Expect(err).ToNot(HaveOccurred())
+					eventCount++
+
+					// Check for content block delta events
+					switch event.AsAny().(type) {
+					case anthropic.ContentBlockDeltaEvent:
+						hasContentDelta = true
+					}
+				}
+
+				Expect(stream.Err()).ToNot(HaveOccurred())
+				Expect(eventCount).To(BeNumerically(">", 0))
+				Expect(hasContentDelta).To(BeTrue())
+
+				// Check accumulated message
+				Expect(message.Content).ToNot(BeEmpty())
+				// Role is a constant type that defaults to "assistant"
+				Expect(string(message.Role)).To(Equal("assistant"))
+			})
+
+			It("streams with system prompt", func() {
+				stream := client.Messages.NewStreaming(context.TODO(), anthropic.MessageNewParams{
+					Model:     "gpt-4",
+					MaxTokens: 1024,
+					System: []anthropic.TextBlockParam{
+						{Text: "You are a helpful assistant."},
+					},
+					Messages: []anthropic.MessageParam{
+						anthropic.NewUserMessage(anthropic.NewTextBlock("Say hello")),
+					},
+				})
+
+				message := anthropic.Message{}
+				for stream.Next() {
+					event := stream.Current()
+					err := message.Accumulate(event)
+					Expect(err).ToNot(HaveOccurred())
+				}
+
+				Expect(stream.Err()).ToNot(HaveOccurred())
+				Expect(message.Content).ToNot(BeEmpty())
+			})
+		})
+	})
+})