Add JSON serialization to LLM message types
Message, Part (Text/Image/File), ToolCall, FunctionCall, and Usage now round-trip through JSON. Message uses a type-discriminated envelope for the Part interface. Required for checkpoint persistence. Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>
This commit is contained in:
Aurélien Sibiril
@@ -65,8 +65,8 @@ type (
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FinishReason string
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Usage struct {
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InputTokens int
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OutputTokens int
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InputTokens int `json:"input_tokens"`
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OutputTokens int `json:"output_tokens"`
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}
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ChatCompletionResponse struct {
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@@ -14,9 +14,11 @@
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package llm
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import "strings"
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import "encoding/json"
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import (
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"encoding/json"
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"fmt"
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"strings"
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)
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type (
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Message struct {
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@@ -27,13 +29,13 @@ type (
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}
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ToolCall struct {
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ID string
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Function FunctionCall
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ID string `json:"id"`
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Function FunctionCall `json:"function"`
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}
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FunctionCall struct {
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Name string
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Arguments string // JSON-encoded arguments
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Name string `json:"name"`
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Arguments string `json:"arguments"`
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}
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Tool struct {
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@@ -43,6 +45,124 @@ type (
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}
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)
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type partEnvelope struct {
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Type string `json:"type"`
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// TextPart and ThinkingPart share the Text field.
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Text string `json:"text,omitempty"`
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// ImagePart fields
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URL string `json:"url,omitempty"`
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// FilePart fields
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Data string `json:"data,omitempty"`
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MimeType string `json:"mime_type,omitempty"`
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Filename string `json:"filename,omitempty"`
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// ThinkingPart fields
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Signature string `json:"signature,omitempty"`
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}
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type messageJSON struct {
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Role Role `json:"role"`
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Parts []partEnvelope `json:"parts,omitempty"`
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ToolCalls []toolCallJSON `json:"tool_calls,omitempty"`
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ToolCallID string `json:"tool_call_id,omitempty"`
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}
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type toolCallJSON struct {
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ID string `json:"id"`
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Function functionCallJSON `json:"function"`
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}
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type functionCallJSON struct {
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Name string `json:"name"`
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Arguments string `json:"arguments"`
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}
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func (m Message) MarshalJSON() ([]byte, error) {
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mj := messageJSON{
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Role: m.Role,
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ToolCallID: m.ToolCallID,
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}
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if len(m.ToolCalls) > 0 {
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mj.ToolCalls = make([]toolCallJSON, len(m.ToolCalls))
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for i, tc := range m.ToolCalls {
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mj.ToolCalls[i] = toolCallJSON{
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ID: tc.ID,
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Function: functionCallJSON{
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Name: tc.Function.Name,
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Arguments: tc.Function.Arguments,
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},
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}
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}
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}
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for _, p := range m.Parts {
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switch v := p.(type) {
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case TextPart:
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mj.Parts = append(mj.Parts, partEnvelope{Type: "text", Text: v.Text})
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case ImagePart:
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mj.Parts = append(mj.Parts, partEnvelope{Type: "image", URL: v.URL})
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case FilePart:
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mj.Parts = append(mj.Parts, partEnvelope{
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Type: "file", Data: v.Data, MimeType: v.MimeType, Filename: v.Filename,
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})
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case ThinkingPart:
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mj.Parts = append(mj.Parts, partEnvelope{Type: "thinking", Text: v.Text, Signature: v.Signature})
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default:
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return nil, fmt.Errorf("cannot marshal unknown Part type %T", p)
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}
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}
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return json.Marshal(mj)
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}
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func (m *Message) UnmarshalJSON(data []byte) error {
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var mj messageJSON
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if err := json.Unmarshal(data, &mj); err != nil {
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return err
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}
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m.Role = mj.Role
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m.ToolCallID = mj.ToolCallID
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if len(mj.ToolCalls) > 0 {
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m.ToolCalls = make([]ToolCall, len(mj.ToolCalls))
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for i, tc := range mj.ToolCalls {
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m.ToolCalls[i] = ToolCall{
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ID: tc.ID,
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Function: FunctionCall{
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Name: tc.Function.Name,
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Arguments: tc.Function.Arguments,
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},
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}
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}
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} else {
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m.ToolCalls = nil
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}
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if len(mj.Parts) == 0 {
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m.Parts = nil
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return nil
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}
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m.Parts = make([]Part, len(mj.Parts))
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for i, env := range mj.Parts {
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switch env.Type {
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case "text":
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m.Parts[i] = TextPart{Text: env.Text}
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case "image":
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m.Parts[i] = ImagePart{URL: env.URL}
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case "file":
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m.Parts[i] = FilePart{Data: env.Data, MimeType: env.MimeType, Filename: env.Filename}
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case "thinking":
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m.Parts[i] = ThinkingPart{Text: env.Text, Signature: env.Signature}
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default:
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return fmt.Errorf("cannot unmarshal unknown Part type %q", env.Type)
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}
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}
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return nil
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}
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func (m Message) Text() string {
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var s strings.Builder
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for _, p := range m.Parts {
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103
pkg/llm/message_test.go
Normal file
103
pkg/llm/message_test.go
Normal file
@@ -0,0 +1,103 @@
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// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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// PERFORMANCE OF THIS SOFTWARE.
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package llm
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import (
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"encoding/json"
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"testing"
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"github.com/stretchr/testify/assert"
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"github.com/stretchr/testify/require"
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)
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func TestMessageJSONRoundTrip(t *testing.T) {
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t.Parallel()
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tests := []struct {
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name string
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msg Message
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}{
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{
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name: "text only",
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msg: Message{
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Role: RoleUser,
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Parts: []Part{TextPart{Text: "hello"}},
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},
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},
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{
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name: "image part",
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msg: Message{
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Role: RoleUser,
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Parts: []Part{ImagePart{URL: "https://example.com/img.png"}},
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},
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},
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{
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name: "file part",
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msg: Message{
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Role: RoleUser,
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Parts: []Part{FilePart{
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Data: "aGVsbG8=", MimeType: "text/plain", Filename: "hello.txt",
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}},
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},
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},
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{
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name: "mixed parts",
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msg: Message{
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Role: RoleUser,
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Parts: []Part{
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TextPart{Text: "see attached"},
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FilePart{Data: "aGVsbG8=", MimeType: "text/plain", Filename: "hello.txt"},
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},
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},
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},
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{
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name: "assistant with tool calls",
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msg: Message{
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Role: RoleAssistant,
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Parts: []Part{TextPart{Text: "calling tool"}},
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ToolCalls: []ToolCall{{
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ID: "call_1",
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Function: FunctionCall{Name: "search", Arguments: `{"q":"test"}`},
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}},
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},
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},
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{
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name: "tool response",
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msg: Message{
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Role: RoleTool,
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ToolCallID: "call_1",
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Parts: []Part{TextPart{Text: "result"}},
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},
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},
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{
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name: "empty parts",
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msg: Message{Role: RoleAssistant},
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},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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t.Parallel()
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data, err := json.Marshal(tt.msg)
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require.NoError(t, err)
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var got Message
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err = json.Unmarshal(data, &got)
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require.NoError(t, err)
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assert.Equal(t, tt.msg, got)
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})
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}
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}
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@@ -20,17 +20,17 @@ type (
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}
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TextPart struct {
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Text string
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Text string `json:"text"`
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}
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ImagePart struct {
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URL string
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URL string `json:"url"`
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}
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FilePart struct {
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Data string // base64-encoded content
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MimeType string // e.g. "application/pdf", "text/csv", "image/png"
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Filename string
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Data string `json:"data"` // base64-encoded content
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MimeType string `json:"mime_type"` // e.g. "application/pdf", "text/csv", "image/png"
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Filename string `json:"filename"`
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}
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ThinkingPart struct {
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