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{
CepisHttp - the transport the Cepis unit sits on.
One function, one GET, no state. Everything above it (retrying, backoff,
turning statuses into exceptions) lives in the Cepis unit, so swapping the
HTTP implementation touches only this file.
Free Pascal uses `fphttpclient`, which ships with the compiler. HTTPS needs
the `opensslsockets` unit linked in - it is, right here - and OpenSSL
present at run time, which is what makes an `https://` base URL work at all.
A Delphi branch built on `System.Net.HttpClient` is provided for source
compatibility. It has never been compiled: this library is developed and
tested with Free Pascal.
}
unit CepisHttp;
{$IFDEF FPC}
{$MODE OBJFPC}
{$H+}
{$ENDIF}
interface
uses
SysUtils, Classes;
type
{
The outcome of one GET.
`Failed` separates the two kinds of answer. When it is True the request
never completed - DNS, refused connection, timeout, TLS - and only
`ErrorMessage` is meaningful. When it is False the server answered, and
`Status` holds what it answered, including 4xx and 5xx: those are answers,
not failures, and the layer above decides what they mean.
`Body` carries the response bytes decoded as UTF-8, which is what the API
sends. `RetryAfter` is the raw `Retry-After` header, unparsed, or empty.
}
TCepisHttpResponse = record
Status: Integer;
Body: string;
RetryAfter: string;
Failed: Boolean;
ErrorMessage: string;
end;
{
Perform a single GET and describe what came back.
Never raises: a transport failure comes back as `Failed = True`. Retrying is
the caller's business.
`ATimeoutMS` bounds each socket operation - the connect, and each read - not
the call as a whole.
}
function CepisHttpGet(const AURL, AUserAgent, AAccept: string;
ATimeoutMS: Integer): TCepisHttpResponse;
implementation
uses
{$IFDEF FPC}
fphttpclient, opensslsockets;
{$ELSE}
System.Net.HttpClient, System.Net.URLClient;
{$ENDIF}
{$IFDEF FPC}
function CepisHttpGet(const AURL, AUserAgent, AAccept: string;
ATimeoutMS: Integer): TCepisHttpResponse;
var
Client: TFPHTTPClient;
Buffer: TMemoryStream;
begin
Result.Status := 0;
Result.Body := '';
Result.RetryAfter := '';
Result.Failed := False;
Result.ErrorMessage := '';
Buffer := TMemoryStream.Create;
try
Client := TFPHTTPClient.Create(nil);
try
Client.AllowRedirect := True;
Client.ConnectTimeout := ATimeoutMS;
Client.IOTimeout := ATimeoutMS;
Client.AddHeader('User-Agent', AUserAgent);
Client.AddHeader('Accept', AAccept);
Client.AddHeader('Accept-Encoding', 'identity');
try
Client.HTTPMethod('GET', AURL, Buffer, []);
Result.Status := Client.ResponseStatusCode;
SetLength(Result.Body, Buffer.Size);
if Buffer.Size > 0 then
Move(Buffer.Memory^, Result.Body[1], Buffer.Size);
if Assigned(Client.ResponseHeaders) then
Result.RetryAfter :=
TFPHTTPClient.GetHeader(Client.ResponseHeaders, 'Retry-After');
except
on E: Exception do
begin
Result.Failed := True;
Result.Status := 0;
Result.Body := '';
Result.RetryAfter := '';
Result.ErrorMessage := E.ClassName + ': ' + E.Message;
end;
end;
finally
Client.Free;
end;
finally
Buffer.Free;
end;
end;
{$ELSE}
function CepisHttpGet(const AURL, AUserAgent, AAccept: string;
ATimeoutMS: Integer): TCepisHttpResponse;
var
Client: THTTPClient;
Response: IHTTPResponse;
Buffer: TMemoryStream;
Payload: TBytes;
begin
Result.Status := 0;
Result.Body := '';
Result.RetryAfter := '';
Result.Failed := False;
Result.ErrorMessage := '';
Buffer := TMemoryStream.Create;
try
Client := THTTPClient.Create;
try
Client.ConnectionTimeout := ATimeoutMS;
Client.ResponseTimeout := ATimeoutMS;
Client.UserAgent := AUserAgent;
Client.HandleRedirects := True;
try
Response := Client.Get(AURL, Buffer,
[TNetHeader.Create('Accept', AAccept),
TNetHeader.Create('Accept-Encoding', 'identity')]);
Result.Status := Response.StatusCode;
SetLength(Payload, Buffer.Size);
if Buffer.Size > 0 then
begin
Buffer.Position := 0;
Buffer.ReadBuffer(Payload[0], Buffer.Size);
end;
Result.Body := TEncoding.UTF8.GetString(Payload);
Result.RetryAfter := Response.HeaderValue['Retry-After'];
except
on E: Exception do
begin
Result.Failed := True;
Result.Status := 0;
Result.Body := '';
Result.RetryAfter := '';
Result.ErrorMessage := E.ClassName + ': ' + E.Message;
end;
end;
finally
Client.Free;
end;
finally
Buffer.Free;
end;
end;
{$ENDIF}
end.
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