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sergey-tihon merged 2 commits into from
May 28, 2026
Merged

perf: reduce allocations & reflection in generated operation code #455

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d7f9576
perf: reduce allocations & reflection in generated operation code
sergey-tihon May 28, 2026
feedb5e
test: cover createHttpRequestFromQueryLists and fillHeadersAndCookies
sergey-tihon May 28, 2026
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170 changes: 97 additions & 73 deletions src/SwaggerProvider.DesignTime/OperationCompiler.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ namespace SwaggerProvider.Internal.Compilers
open System
open System.Collections.Generic
open System.Net.Http
open System.Reflection
open System.Text.Json

open Microsoft.FSharp.Quotations
Expand Down Expand Up @@ -60,6 +61,44 @@ type PayloadType =

/// Object for compiling operations.
type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler, ignoreControllerPrefix, ignoreOperationId, asAsync: bool) =
let toParamMethod =
match <@@ RuntimeHelpers.toParam(null) @@> with
| Call(None, m, _) -> m
| _ -> failwith "Cannot extract toParam MethodInfo"

let toQueryParamsMethod =
match <@@ RuntimeHelpers.toQueryParams "" null Unchecked.defaultof<ProvidedApiClientBase> @@> with
| Call(None, m, _) -> m
| _ -> failwith "Cannot extract toQueryParams MethodInfo"

let resolveCastMethod(ownerType: Type) =
ownerType.GetMethods(BindingFlags.Public ||| BindingFlags.Static)
|> Array.tryFind(fun m ->
m.Name = "cast"
&& m.IsGenericMethodDefinition
&& m.GetGenericArguments().Length = 1
&& m.GetParameters().Length = 1)
|> Option.defaultWith(fun () -> failwithf "Cannot extract %s.cast<'T> MethodInfo" ownerType.FullName)

let taskCastMethod = resolveCastMethod typeof<TaskExtensions>
let asyncCastMethod = resolveCastMethod typeof<AsyncExtensions>

let stringPairListExpr(items: (string * string) list) : Expr<(string * string) list> =
let empty = <@ [] @>

(empty, List.rev items)
||> List.fold(fun acc (name, value) ->
let nameExpr = Expr.Value(name, typeof<string>) |> Expr.Cast<string>
let valueExpr = Expr.Value(value, typeof<string>) |> Expr.Cast<string>

<@ (%nameExpr, %valueExpr) :: %acc @>)

let typedListExpr(items: Expr<'T> list) : Expr<'T list> =
let empty = <@ [] @>

(empty, List.rev items)
||> List.fold(fun acc item -> <@ %item :: %acc @>)

let compileOperation (providedMethodName: string) (apiCall: ApiCall) =
let path, pathItem, opTy = apiCall
let operation = pathItem.Operations[opTy]
Expand Down Expand Up @@ -96,7 +135,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
let (|NoMediaType|_|)(content: IDictionary<string, OpenApiMediaType>) =
if isNull content || content.Count = 0 then Some() else None

let payloadTy, payloadMime, parameters, ctArgIndex =
let payloadTy, payloadMime, parameters, ctArgIndex, apiParamByProvidedName =
/// handles de-duplicating Swagger parameter names if the same parameter name
/// appears in multiple locations in a given operation definition.
let uniqueParamName usedNames (param: IOpenApiParameter) =
Expand Down Expand Up @@ -156,8 +195,8 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
|> List.partition(_.Required)

let buildProvidedParameters usedNames (paramList: IOpenApiParameter list) =
((usedNames, []), paramList)
||> List.fold(fun (names, parameters) current ->
((usedNames, [], []), paramList)
||> List.fold(fun (names, parameters, lookup) current ->
let names, paramName = uniqueParamName names current

let paramType =
Expand All @@ -170,15 +209,20 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
let paramDefaultValue = defCompiler.GetDefaultValue paramType
ProvidedParameter(paramName, paramType, false, paramDefaultValue)

(names, providedParam :: parameters))
|> fun (finalNames, ps) -> finalNames, List.rev ps
(names, providedParam :: parameters, (paramName, current) :: lookup))
|> fun (finalNames, ps, lookup) -> finalNames, List.rev ps, List.rev lookup

let namesAfterRequired, requiredProvidedParams =
let namesAfterRequired, requiredProvidedParams, requiredLookup =
buildProvidedParameters Set.empty requiredOpenApiParams

let _, optionalProvidedParams =
let _, optionalProvidedParams, optionalLookup =
buildProvidedParameters namesAfterRequired optionalOpenApiParams

let apiParamByProvidedName =
requiredLookup @ optionalLookup
|> List.choose(fun (paramName, param) -> if param.In.HasValue then Some(paramName, param) else None)
|> Map.ofList

let ctArgIndex, parameters =
let scope = UniqueNameGenerator()

Expand All @@ -196,7 +240,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,

ctArgIndex, requiredProvidedParams @ optionalProvidedParams @ [ ctParam ]

payloadTy, payloadTy.ToMediaType(), parameters, ctArgIndex
payloadTy, payloadTy.ToMediaType(), parameters, ctArgIndex, apiParamByProvidedName

// find the inner type value
let okResponse =
Expand Down Expand Up @@ -258,6 +302,12 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
|> Seq.toArray
|> Array.unzip

let fixedHeaders =
[ if not(isNull payloadMime) then
"Content-Type", payloadMime
if not(isNull retMime) then
"Accept", retMime ]

let m =
ProvidedMethod(
providedMethodName,
Expand All @@ -271,13 +321,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,

let httpMethod = opTy.ToString()

let headers =
<@
[ if not(isNull payloadMime) then
"Content-Type", payloadMime
if not(isNull retMime) then
"Accept", retMime ]
@>
let headers = stringPairListExpr fixedHeaders

// Locates parameters matching the arguments
let mutable payloadExp = None
Expand All @@ -298,14 +342,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
apiArgs
|> List.choose (function
| ShapeVar sVar as expr ->
let param =
openApiParameters
|> Seq.tryFind(fun x ->
// pain point: we have to make sure that the set of names we search for here are the same as the set of names generated when we make `parameters` above
let baseName = niceCamelName x.Name
baseName = sVar.Name || (unambiguousName x) = sVar.Name)

match param with
match apiParamByProvidedName |> Map.tryFind sVar.Name with
| Some(par) -> Some(par, expr)
| _ ->
let payloadType = PayloadType.Parse sVar.Name
Expand All @@ -324,31 +361,21 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
// object across all calls, causing "duplicate key" exceptions in ProvidedTypes
// when the same helper is called for multiple parameters in one operation.
// Instead, build the call expression directly without an intermediate binding.
let toParamMethod =
match <@@ RuntimeHelpers.toParam(null) @@> with
| Call(None, m, _) -> m
| _ -> failwith "Cannot extract toParam MethodInfo"

let coerceString exp =
let obj = Expr.Coerce(exp, typeof<obj>)
Expr.Call(toParamMethod, [ obj ]) |> Expr.Cast<string>

let toQueryParamsMethod =
match <@@ RuntimeHelpers.toQueryParams "" null (%this) @@> with
| Call(None, m, _) -> m
| _ -> failwith "Cannot extract toQueryParams MethodInfo"

let rec coerceQueryString name expr =
let obj = Expr.Coerce(expr, typeof<obj>)

Expr.Call(toQueryParamsMethod, [ Expr.Value name; obj; this ])
|> Expr.Cast<(string * string) list>

// Partitions arguments based on their locations
let path, queryParams, headers =
let path, queryParams, headers, cookies =
((<@ path @>, <@ [] @>, headers, <@ [] @>), parameters)
||> List.fold(fun (path, query, headers, cookies) (param: IOpenApiParameter, valueExpr) ->
let path, queryParamLists, headers, cookies =
let path, queryParamLists, headers, cookies =
((<@ path @>, [], headers, <@ [] @>), parameters)
||> List.fold(fun (path, queryParamLists, headers, cookies) (param: IOpenApiParameter, valueExpr) ->
if param.In.HasValue then
let name = param.Name

Expand All @@ -357,44 +384,32 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
let value = coerceString valueExpr
let pattern = $"{{%s{name}}}"
let path' = <@ (%path).Replace(pattern, %value) @>
(path', query, headers, cookies)
(path', queryParamLists, headers, cookies)
| ParameterLocation.Query ->
let listValues = coerceQueryString name valueExpr
let query' = <@ List.append %query %listValues @>
(path, query', headers, cookies)
(path, listValues :: queryParamLists, headers, cookies)
| ParameterLocation.Header ->
let value = coerceString valueExpr
let headers' = <@ (name, %value) :: (%headers) @>
(path, query, headers', cookies)
(path, queryParamLists, headers', cookies)
| ParameterLocation.Cookie ->
let value = coerceString valueExpr
let cookies' = <@ (name, %value) :: (%cookies) @>
(path, query, headers, cookies')
(path, queryParamLists, headers, cookies')
| x -> failwithf $"Unsupported parameter location '%A{x}'"
else
failwithf "This should not happen, payload expression is already parsed")

let headers' =
<@
let cookieHeader =
%cookies
|> Seq.filter(snd >> isNull >> not)
|> Seq.map(fun (name, value) -> $"{name}={value}")
|> String.concat ";"

if String.IsNullOrEmpty cookieHeader then
%headers
else
("Cookie", cookieHeader) :: (%headers)
@>

(path, queryParams, headers')
path, List.rev queryParamLists, headers, cookies

let queryParamLists = typedListExpr queryParamLists

let httpRequestMessage =
<@
let msg = RuntimeHelpers.createHttpRequest httpMethod %path %queryParams
RuntimeHelpers.fillHeaders msg %headers
let msg =
RuntimeHelpers.createHttpRequestFromQueryLists httpMethod %path %queryParamLists

RuntimeHelpers.fillHeadersAndCookies msg %headers %cookies
msg
@>

Expand Down Expand Up @@ -441,7 +456,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
let action =
<@ (%this).CallAsync(%httpRequestMessageWithPayload, errorCodes, errorDescriptions, %ct) @>

let responseObj =
let responseObj() =
let innerReturnType = defaultArg retTy null

<@
Expand All @@ -455,7 +470,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
}
@>

let responseStream =
let responseStream() =
<@
let x = %action
let ct = %ct
Expand All @@ -467,7 +482,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
}
@>

let responseString =
let responseString() =
<@
let x = %action
let ct = %ct
Expand All @@ -479,7 +494,7 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
}
@>

let responseUnit =
let responseUnit() =
<@
let x = %action

Expand All @@ -489,27 +504,36 @@ type OperationCompiler(schema: OpenApiDocument, defCompiler: DefinitionCompiler,
}
@>

// if we're an async method, then we can just return the above, coerced to the overallReturnType.
// if we're not async, then run that^ through Async.RunSynchronously before doing the coercion.
// Build only the response quotation needed for this operation's return shape.
// For typed JSON responses, emit direct generic cast calls so generated clients
// do not pay MethodInfo.Invoke costs on every API call.
if not asAsync then
match retTy with
| None -> responseUnit.Raw
| Some t when t = typeof<IO.Stream> -> <@ %responseStream @>.Raw
| None -> (responseUnit()).Raw
| Some t when t = typeof<IO.Stream> -> <@ %(responseStream()) @>.Raw
| Some t ->
match retMime with
| TextReturn _ -> <@ %responseString @>.Raw
| _ -> Expr.Coerce(<@ RuntimeHelpers.taskCast t %responseObj @>, overallReturnType)
| TextReturn _ -> <@ %(responseString()) @>.Raw
| _ ->
let castMethod = ProvidedTypeBuilder.MakeGenericMethod(taskCastMethod, [ t ])

Expr.Call(castMethod, [ responseObj() ])
|> fun e -> Expr.Coerce(e, overallReturnType)
else
let awaitTask t =
<@ Async.AwaitTask(%t) @>

match retTy with
| None -> (awaitTask responseUnit).Raw
| Some t when t = typeof<IO.Stream> -> <@ %(awaitTask responseStream) @>.Raw
| None -> (awaitTask(responseUnit())).Raw
| Some t when t = typeof<IO.Stream> -> <@ %(awaitTask(responseStream())) @>.Raw
| Some t ->
match retMime with
| TextReturn _ -> <@ %(awaitTask responseString) @>.Raw
| _ -> Expr.Coerce(<@ RuntimeHelpers.asyncCast t %(awaitTask responseObj) @>, overallReturnType)
| TextReturn _ -> <@ %(awaitTask(responseString())) @>.Raw
| _ ->
let castMethod = ProvidedTypeBuilder.MakeGenericMethod(asyncCastMethod, [ t ])

Expr.Call(castMethod, [ awaitTask(responseObj()) ])
|> fun e -> Expr.Coerce(e, overallReturnType)
)

let xmlDoc =
Expand Down
11 changes: 6 additions & 5 deletions src/SwaggerProvider.DesignTime/Provider.OpenApiClient.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -30,13 +30,14 @@ type public OpenApiClientTypeProvider(cfg: TypeProviderConfig) as this =
// check we contain a copy of runtime files, and are not referencing the runtime DLL
do assert (typeof<ProvidedApiClientBase>.Assembly.GetName().Name = asm.GetName().Name)

let buildStringListExpr(items: string list) : Expr =
let stringListNilCase, stringListConsCase =
let cases = FSharpType.GetUnionCases typeof<string list>
let nilCase = cases |> Array.find(fun c -> c.Name = "Empty")
let consCase = cases |> Array.find(fun c -> c.Name = "Cons")
let nil = Expr.NewUnionCase(nilCase, [])
cases |> Array.find(fun c -> c.Name = "Empty"), cases |> Array.find(fun c -> c.Name = "Cons")

let buildStringListExpr(items: string list) : Expr =
let nil = Expr.NewUnionCase(stringListNilCase, [])

List.foldBack (fun (s: string) acc -> Expr.NewUnionCase(consCase, [ Expr.Value(s, typeof<string>); acc ])) items nil
List.foldBack (fun (s: string) acc -> Expr.NewUnionCase(stringListConsCase, [ Expr.Value(s, typeof<string>); acc ])) items nil

let myParamType =
let t =
Expand Down
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