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fix(ai-proxy): correct Anthropic Messages to OpenAI Chat request conversion #13674

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Merged
nic-6443 merged 7 commits into from
Jul 9, 2026
+813 −194
Merged

fix(ai-proxy): correct Anthropic Messages to OpenAI Chat request conversion #13674

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eaf1610
fix(ai-proxy): correct Anthropic Messages to OpenAI Chat request conv…
nic-6443 Jul 8, 2026
a0c05ed
fix(ai-proxy): keep OpenAI tool names unique when sanitizing
nic-6443 Jul 8, 2026
a05c7dc
fix(ai-proxy): follow the Anthropic spec for effort and structured ou…
nic-6443 Jul 8, 2026
15b91f9
fix(ai-proxy): map Anthropic xhigh effort to OpenAI xhigh
nic-6443 Jul 8, 2026
4d8a559
fix(ai-proxy): align effort and structured outputs with the reference…
nic-6443 Jul 8, 2026
6f12b1e
fix(ai-proxy): align tool naming, effort buckets and message shaping
nic-6443 Jul 8, 2026
f97b8e1
fix(ai-proxy): emit an empty `required` as a JSON array
nic-6443 Jul 8, 2026
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263 changes: 154 additions & 109 deletions apisix/plugins/ai-protocols/converters/anthropic-messages-to-openai-chat.lua
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@
local core = require("apisix.core")
local table = table
local type = type
local next = next
local pairs = pairs
local ipairs = ipairs
local tostring = tostring
Expand Down Expand Up @@ -62,6 +63,42 @@ local function sanitize_tool_name(name)
end


-- Map an Anthropic tool name to the name used on the OpenAI side, recording
-- the mapping so the response converter can restore the original name.
-- `maps.forward` is original → openai, `maps.reverse` is openai → original.
-- Both the `tools` array and the `tool_use` blocks in the conversation history
-- go through here, so a tool always carries the same name in both places.
local function openai_tool_name(name, maps)
local mapped = maps.forward[name]
if mapped then
return mapped
end

if string_len(name) <= TOOL_NAME_MAX_LEN
and not ngx_re_find(name, "[^a-zA-Z0-9_-]", "jo") then
return name
end
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local sanitized = sanitize_tool_name(name)
-- Disambiguate collisions by appending a numeric suffix
if maps.reverse[sanitized] then
local suffix = 2
local candidate
repeat
local suffix_str = "_" .. suffix
local max_base = TOOL_NAME_MAX_LEN - string_len(suffix_str)
candidate = string_sub(sanitized, 1, max_base) .. suffix_str
suffix = suffix + 1
until not maps.reverse[candidate]
sanitized = candidate
end

maps.reverse[sanitized] = name
maps.forward[name] = sanitized
return sanitized
end


-- SSE event helpers
local function make_sse_event(event_type, data)
return { type = event_type, data = core.json.encode(data) }
Expand Down Expand Up @@ -165,14 +202,33 @@ local function convert_tool_choice(tc)
end


-- Anthropic output_config.effort → OpenAI reasoning_effort.
-- OpenAI Chat Completions has no "xhigh"/"max" level, so both clamp to "high".
local effort_map = {
low = "low",
medium = "medium",
high = "high",
xhigh = "high",
max = "high",
}


-- Convert Anthropic thinking config to OpenAI reasoning_effort.
local function convert_thinking_config(thinking)
-- `thinking.type` is one of "enabled", "disabled" or "adaptive". With
-- "adaptive" the depth is driven by output_config.effort instead of
-- budget_tokens.
local function convert_thinking_config(thinking, output_config)
if type(thinking) ~= "table" then
return nil
end
if thinking.type == "disabled" then
return nil

if thinking.type == "adaptive" then
if type(output_config) == "table" and type(output_config.effort) == "string" then
return effort_map[output_config.effort] or "medium"
end
return "medium"
end

if thinking.type ~= "enabled" then
return nil
end
Expand Down Expand Up @@ -291,7 +347,8 @@ function _M.convert_request(request_table, ctx)

-- thinking → reasoning_effort
if request_table.thinking then
local effort = convert_thinking_config(request_table.thinking)
local effort = convert_thinking_config(request_table.thinking,
request_table.output_config)
if effort then
openai_body.reasoning_effort = effort
end
Expand All @@ -310,15 +367,24 @@ function _M.convert_request(request_table, ctx)
end
end

-- response_format from output_config or output_format
local output_cfg = request_table.output_config or request_table.output_format
if type(output_cfg) == "table" then
if output_cfg.type == "json_schema" and output_cfg.json_schema then
-- Structured outputs → response_format. The schema lives in
-- `output_config.format` (GA) or in the top-level `output_format` (beta),
-- both shaped as { type = "json_schema", schema = <json schema> }.
local output_format = request_table.output_format
if type(output_format) ~= "table" and type(request_table.output_config) == "table" then
output_format = request_table.output_config.format
end
if type(output_format) == "table" then
if output_format.type == "json_schema" and type(output_format.schema) == "table" then
openai_body.response_format = {
type = "json_schema",
json_schema = output_cfg.json_schema,
json_schema = {
name = "structured_output",
schema = output_format.schema,
strict = true,
},
}
elseif output_cfg.type == "json_object" or output_cfg.type == "json" then
elseif output_format.type == "json_object" then
openai_body.response_format = { type = "json_object" }
end
end
Expand All @@ -334,7 +400,62 @@ function _M.convert_request(request_table, ctx)
openai_body.service_tier = request_table.service_tier
end

-- 1. System prompt
-- 1. Convert tools (only when non-empty). This runs before the messages so
-- that the `tool_use` blocks in the conversation history are renamed with
-- the same mapping as the tool definitions.
local tool_name_maps = { forward = {}, reverse = {} }
if type(request_table.tools) == "table" and #request_table.tools > 0 then
local openai_tools = {}
for _, tool in ipairs(request_table.tools) do
if type(tool) ~= "table" then
goto CONTINUE_TOOL
end

-- Skip Anthropic built-in tools (they have type but no input_schema)
if type(tool.type) == "string" then
local is_builtin = false
for _, prefix in ipairs(BUILTIN_TOOL_PREFIXES) do
if string_sub(tool.type, 1, string_len(prefix)) == prefix then
is_builtin = true
break
end
end
if is_builtin then
core.log.debug("dropping Anthropic built-in tool '", tool.type,
"': not supported by OpenAI upstream")
goto CONTINUE_TOOL
end
end

if type(tool.name) ~= "string" or tool.name == "" then
goto CONTINUE_TOOL
end

local oai_tool = {
type = "function",
["function"] = {
name = openai_tool_name(tool.name, tool_name_maps),
description = tool.description,
parameters = tool.input_schema,
},
}
table.insert(openai_tools, oai_tool)
::CONTINUE_TOOL::
end
if #openai_tools > 0 then
openai_body.tools = openai_tools
end
-- Fix tool_choice to use the sanitized name if applicable
if type(openai_body.tool_choice) == "table"
and openai_body.tool_choice.type == "function" then
local tc_func = openai_body.tool_choice["function"]
if tc_func and type(tc_func.name) == "string" then
tc_func.name = tool_name_maps.forward[tc_func.name] or tc_func.name
end
end
end

-- 2. System prompt
local messages = {}
if request_table.system then
local sys_msg = convert_system(request_table.system)
Expand All @@ -343,7 +464,7 @@ function _M.convert_request(request_table, ctx)
end
end

-- 2. Convert messages
-- 3. Convert messages
for i, msg in ipairs(request_table.messages) do
if type(msg) ~= "table" or type(msg.role) ~= "string" then
return nil, "invalid message at index " .. i
Expand Down Expand Up @@ -388,7 +509,7 @@ function _M.convert_request(request_table, ctx)
id = block.id,
type = "function",
["function"] = {
name = block.name,
name = openai_tool_name(block.name, tool_name_maps),
arguments = core.json.encode(block.input or {})
}
})
Expand Down Expand Up @@ -441,23 +562,30 @@ function _M.convert_request(request_table, ctx)
::CONTINUE_BLOCK::
end

-- Emit tool_results as separate messages
-- Emit tool_results as separate messages. OpenAI requires every `tool`
-- message to immediately follow the assistant message that carries the
-- matching tool_calls, so anything else in this Anthropic message has
-- to be emitted after them, not before.
if #tool_results > 0 then
-- If there's text alongside tool_results, emit it first
for _, tr in ipairs(tool_results) do
table.insert(messages, tr)
end

if #content_parts > 0 then
local text_content = ""
for _, p in ipairs(content_parts) do
if p.type == "text" then
local content
if has_multimodal then
content = content_parts
else
local text_content = ""
for _, p in ipairs(content_parts) do
text_content = text_content .. (p.text or "")
end
content = text_content ~= "" and text_content or nil
end
if text_content ~= "" then
table.insert(messages, { role = msg.role, content = text_content })
if content then
table.insert(messages, { role = msg.role, content = content })
end
end
for _, tr in ipairs(tool_results) do
table.insert(messages, tr)
end
goto CONTINUE
end

Expand Down Expand Up @@ -491,92 +619,9 @@ function _M.convert_request(request_table, ctx)
end
openai_body.messages = messages

-- 3. Convert tools (only when non-empty)
if type(request_table.tools) == "table" and #request_table.tools > 0 then
local openai_tools = {}
local tool_name_map -- lazily created if truncation needed
for _, tool in ipairs(request_table.tools) do
if type(tool) ~= "table" then
goto CONTINUE_TOOL
end

-- Skip Anthropic built-in tools (they have type but no input_schema)
if type(tool.type) == "string" then
local is_builtin = false
for _, prefix in ipairs(BUILTIN_TOOL_PREFIXES) do
if string_sub(tool.type, 1, string_len(prefix)) == prefix then
is_builtin = true
break
end
end
if is_builtin then
core.log.debug("dropping Anthropic built-in tool '", tool.type,
"': not supported by OpenAI upstream")
goto CONTINUE_TOOL
end
end

if type(tool.name) ~= "string" or tool.name == "" then
goto CONTINUE_TOOL
end

-- Sanitize tool name for OpenAI compatibility
local oai_name = tool.name
if string_len(oai_name) > TOOL_NAME_MAX_LEN
or ngx_re_find(oai_name, "[^a-zA-Z0-9_-]", "jo") then
local sanitized = sanitize_tool_name(oai_name)
if sanitized ~= oai_name then
if not tool_name_map then
tool_name_map = {}
end
-- Disambiguate collisions by appending numeric suffix
if tool_name_map[sanitized] then
local suffix = 2
local candidate
repeat
local suffix_str = "_" .. suffix
local max_base = TOOL_NAME_MAX_LEN - string_len(suffix_str)
candidate = string_sub(sanitized, 1, max_base) .. suffix_str
suffix = suffix + 1
until not tool_name_map[candidate]
sanitized = candidate
end
tool_name_map[sanitized] = oai_name
oai_name = sanitized
end
end

local oai_tool = {
type = "function",
["function"] = {
name = oai_name,
description = tool.description,
parameters = tool.input_schema,
},
}
table.insert(openai_tools, oai_tool)
::CONTINUE_TOOL::
end
if #openai_tools > 0 then
openai_body.tools = openai_tools
end
-- Store tool name mapping in ctx for response restoration
if tool_name_map then
ctx.anthropic_tool_name_map = tool_name_map
-- Fix tool_choice to use sanitized name if applicable
if type(openai_body.tool_choice) == "table"
and openai_body.tool_choice.type == "function" then
local tc_func = openai_body.tool_choice["function"]
if tc_func and type(tc_func.name) == "string" then
for sanitized, original in pairs(tool_name_map) do
if original == tc_func.name then
tc_func.name = sanitized
break
end
end
end
end
end
-- Store tool name mapping in ctx for response restoration
if next(tool_name_maps.reverse) then
ctx.anthropic_tool_name_map = tool_name_maps.reverse
end

-- tool_choice and parallel_tool_calls are only valid alongside a non-empty
Expand Down
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