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mcp: don't omit required fields in ImageContent and AudioContent #95

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Merged
merged 1 commit into from
Jul 19, 2025
+46 −6
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mcp: don't omit required fields in ImageContent and AudioContent #95

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36 changes: 30 additions & 6 deletions mcp/content.go
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Original file line number Diff line number Diff line change
Expand Up @@ -58,13 +58,25 @@ type ImageContent struct {
}

func (c *ImageContent) MarshalJSON() ([]byte, error) {
return json.Marshal(&wireContent{
// Custom wire format to ensure required fields are always included, even when empty.
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It looks like these two functions are almost identical. Factor out into a single function. It looks to me that that function's args are the type (image or audio) and the data.

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We can if you think it's important.

Two copies of something doesn't feel like a strong deduplication signal to me given that it will split the currently very clear schema mapping into a function that abstracts away half of the type.

If you think this is a blocker, I'll refactor, since I'd prefer the sdk is correct regardless of the code inside.

data := c.Data
if data == nil {
data = []byte{}
}
wire := struct {
Type string `json:"type"`
MIMEType string `json:"mimeType"`
Data []byte `json:"data"`
Meta Meta `json:"_meta,omitempty"`
Annotations *Annotations `json:"annotations,omitempty"`
}{
Type: "image",
MIMEType: c.MIMEType,
Data: c.Data,
Data: data,
Meta: c.Meta,
Annotations: c.Annotations,
})
}
return json.Marshal(wire)
}

func (c *ImageContent) fromWire(wire *wireContent) {
Expand All @@ -83,13 +95,25 @@ type AudioContent struct {
}

func (c AudioContent) MarshalJSON() ([]byte, error) {
return json.Marshal(&wireContent{
// Custom wire format to ensure required fields are always included, even when empty.
data := c.Data
if data == nil {
data = []byte{}
}
wire := struct {
Type string `json:"type"`
MIMEType string `json:"mimeType"`
Data []byte `json:"data"`
Meta Meta `json:"_meta,omitempty"`
Annotations *Annotations `json:"annotations,omitempty"`
}{
Type: "audio",
MIMEType: c.MIMEType,
Data: c.Data,
Data: data,
Meta: c.Meta,
Annotations: c.Annotations,
})
}
return json.Marshal(wire)
}

func (c *AudioContent) fromWire(wire *wireContent) {
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16 changes: 16 additions & 0 deletions mcp/content_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,14 @@ func TestContent(t *testing.T) {
},
`{"type":"image","mimeType":"image/png","data":"YTFiMmMz"}`,
},
{
&mcp.ImageContent{MIMEType: "image/png", Data: []byte{}},
`{"type":"image","mimeType":"image/png","data":""}`,
},
{
&mcp.ImageContent{Data: []byte("test")},
`{"type":"image","mimeType":"","data":"dGVzdA=="}`,
},
{
&mcp.ImageContent{
Data: []byte("a1b2c3"),
Expand All @@ -61,6 +69,14 @@ func TestContent(t *testing.T) {
},
`{"type":"audio","mimeType":"audio/wav","data":"YTFiMmMz"}`,
},
{
&mcp.AudioContent{MIMEType: "audio/wav", Data: []byte{}},
`{"type":"audio","mimeType":"audio/wav","data":""}`,
},
{
&mcp.AudioContent{Data: []byte("test")},
`{"type":"audio","mimeType":"","data":"dGVzdA=="}`,
},
{
&mcp.AudioContent{
Data: []byte("a1b2c3"),
Expand Down
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