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feat: add support for MCP HTTP streaming #975

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Merged
merged 2 commits into from
May 27, 2025
Merged

feat: add support for MCP HTTP streaming #975

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bb5f918
feat: add support for MCP HTTP streaming
thedadams May 27, 2025
916a2c2
chore: bump mcp dependency
thedadams May 27, 2025
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26 changes: 19 additions & 7 deletions pkg/mcp/loader.go
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ import (
"github.com/gptscript-ai/gptscript/pkg/mvl"
"github.com/gptscript-ai/gptscript/pkg/types"
"github.com/gptscript-ai/gptscript/pkg/version"
"github.com/mark3labs/mcp-go/client"
mcpclient "github.com/mark3labs/mcp-go/client"
"github.com/mark3labs/mcp-go/client/transport"
"github.com/mark3labs/mcp-go/mcp"
)

Expand All @@ -36,7 +37,7 @@ type Local struct {
type Session struct {
ID string
InitResult *mcp.InitializeResult
Client client.MCPClient
Client mcpclient.MCPClient
Config ServerConfig
}

Expand Down Expand Up @@ -117,7 +118,7 @@ func (l *Local) LoadTools(ctx context.Context, server ServerConfig, toolName str
// Reset so we don't start a new MCP server, no reason to if one is already running and the allowed tools change.
server.AllowedTools = nil

session, err := l.loadSession(server)
session, err := l.loadSession(server, true)
if err != nil {
return nil, err
}
Expand Down Expand Up @@ -279,7 +280,7 @@ func (l *Local) sessionToTools(ctx context.Context, session *Session, toolName s
return toolDefs, nil
}

func (l *Local) loadSession(server ServerConfig) (*Session, error) {
func (l *Local) loadSession(server ServerConfig, tryHTTPStreaming bool) (*Session, error) {
id := hash.Digest(server)
l.lock.Lock()
existing, ok := l.sessions[id]
Expand All @@ -294,11 +295,11 @@ func (l *Local) loadSession(server ServerConfig) (*Session, error) {
}

var (
c *client.Client
c *mcpclient.Client
err error
)
if server.Command != "" {
c, err = client.NewStdioMCPClient(server.Command, server.Env, server.Args...)
c, err = mcpclient.NewStdioMCPClient(server.Command, server.Env, server.Args...)
if err != nil {
return nil, fmt.Errorf("failed to create MCP stdio client: %w", err)
}
Expand All @@ -314,7 +315,11 @@ func (l *Local) loadSession(server ServerConfig) (*Session, error) {
headers[k] = v
}

c, err = client.NewSSEMCPClient(url, client.WithHeaders(headers))
if tryHTTPStreaming {
c, err = mcpclient.NewStreamableHttpClient(url, transport.WithHTTPHeaders(headers))
} else {
c, err = mcpclient.NewSSEMCPClient(url, mcpclient.WithHeaders(headers))
}
if err != nil {
return nil, fmt.Errorf("failed to create MCP HTTP client: %w", err)
}
Expand All @@ -333,6 +338,13 @@ func (l *Local) loadSession(server ServerConfig) (*Session, error) {

initResult, err := c.Initialize(ctx, initRequest)
if err != nil {
if server.Command == "" && tryHTTPStreaming {
// The MCP spec indicates that trying to initialize the client for HTTP streaming and checking for an error
// is the recommended way to determine if the server supports HTTP streaming, falling back to SEE.
// Ideally, we can check for a 400-level error, but our client implementation doesn't expose that information.
// Retrying on any error is harmless.
return l.loadSession(server, false)
}
return nil, fmt.Errorf("failed to initialize MCP client: %w", err)
}

Expand Down