c044cdb734`ReadOnlyHint` is a `bool` with omitempty, so the zero value (false) is indistinguishable from unset, and **drops out** of marshaled JSON. The current behavior causes an issue with the OpenAI MCP app submission because they require explicit hints. Consumers that explicitly set `ReadOnlyHint: false` on write tools lose the field on the wire. Removing `omitempty` ensures `false` is always serialized, which matches the MCP spec default. --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com> Co-authored-by: Maciej Kisiel <mkisiel@google.com> Co-authored-by: guglielmoc <guglielmoc@google.com>
88 lines
3.8 KiB
Markdown
88 lines
3.8 KiB
Markdown
# Backwards compatibility and MCPGODEBUG
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According to our compatibility promise, we can't break backward compatibility
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of the SDK API. However, sometimes we need to change the behavior of the SDK
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in a backward-incompatible way in order to fix bugs or security issues.
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In those cases we introduce temporary compatibility parameters, that can be
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used to opt-out of the new behavior. They are usually maintained for two
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minor release cycles and then removed.
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The compatibility parameters are provided via the `MCPGODEBUG` environment
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variable. The value of the variable is a comma-separated list of parameter
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value assignments, e.g.:
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```
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MCPGODEBUG=parameter1=value1,parameter2=value2
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```
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## `MCPGODEBUG` history
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### 1.7.0
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Options listed below were added and will be removed in the 1.9.0 version of the SDK.
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- `customresnotfounderrcode` added. If set to `1`, `ResourceNotFoundError` will
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use the custom error code `-32002` instead of the standard `-32602` (Invalid
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Params), restoring the previous behavior. The default behavior was changed to
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align with SEP-2164 and the JSON-RPC specification.
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- `hintomitempty` added. If set to `1`, `ToolAnnotations` JSON marshaling
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will omit `ReadOnlyHint` and `IdempotentHint` when their value is `false`,
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restoring the previous behavior. The default behavior was changed to always
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serialize these fields, since their Go types are bare `bool` (not `*bool`)
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and omitting `false` made it indistinguishable from unset.
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- `allowsessionsinstateless` added. If set to `1`, stateless streamable HTTP
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servers will read the `Mcp-Session-Id` request header (or generate one via
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`GetSessionID`), set it on response headers, and accept `DELETE` requests,
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restoring the previous behavior. The default behavior was changed so that
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stateless servers ignore session IDs entirely and reject `DELETE` with 405.
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### 1.6.0
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Options listed below were added and will be removed in the 1.8.0 version of the SDK.
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- `seterroroverwrite` added. If set to `1`, `SetError` will always overwrite
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`Content` with the error text, restoring the previous behavior. The default
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behavior was changed to preserve existing `Content` if it has already been
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populated.
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- `enableoriginverification` added. If set to `1`, default (zero-value)
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cross-origin protection will be applied when
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`StreamableHTTPOptions.CrossOriginProtection` is nil, restoring the
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behavior from v1.4.1-v1.5.0. The default behavior was changed to not
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enable cross-origin protection.
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- `disablelocalhostprotection` removal was postponed until 1.8.0, as it is now
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also used in the SSE transport.
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Options below were removed:
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- `jsonescaping`, according to plan,
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- `disablecrossoriginprotection`, it was replaced by
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`enableoriginverification` after the default was changed to not enable
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cross-origin protection.
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### 1.4.1
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Options listed below will be removed in the 1.6.0 version of the SDK.
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- `disablecrossoriginprotection` added. If set to `1`, newly added cross-origin
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protection will be disabled. The default behavior was changed to enable
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cross-origin protection.
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### 1.4.0
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Options listed below will be removed in the 1.6.0 version of the SDK.
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- `jsonescaping` added. If set to `1`, JSON marshaling will preserve the previous
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behavior of escaping HTML characters in JSON strings. The default behavior
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was changed to not escape HTML characters, to be consistent with other SDKs.
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- `disablelocalhostprotection` added. If set to `1`, newly added DNS rebinding
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protection will be disabled. The default behavior was changed to enable DNS rebinding
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protection. The protection can also be disabled by setting the
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`DisableLocalhostProtection` field in the `StreamableHTTPOptions` or
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`SSEOptions` struct to `true`, which is the recommended way to disable
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the protection long term. **Removal of this option was postponed until 1.8.0.**
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