This is not a limitation of **FastAPI**, it's part of the HTTP protocol.

///

## Recap { #recap }

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

            try {
                // Exponential backoff with overflow protection - ensure safe calculation
                if (retryDelayMs > 0) {
                    // Safe calculation preventing overflow: use Math.max(0, retryCount - 1) and limit shift
                    int safeShift = Math.min(MAX_BACKOFF_SHIFT, Math.max(0, retryCount - 1));
                    long multiplier = 1L << safeShift;

	FMOVD	0x8008(R1), F2		// FMOVD	32776(R1), F2		// 3b204091620740fd
	FMOVD	0x1006ff8(R1), F2	// FMOVD	16805880(R1), F2	// 3bfc7f9162ff7ffd

// very large or unaligned offset uses constant pool.
// the encoding cannot be checked as the address of the constant pool is unknown.
// here we only test that they can be assembled.
	MOVB	R1, 0x1000000(R2)	// MOVB		R1, 16777216(R2)

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

pkg net/http, type Transport struct, DialTLS func(string, string) (net.Conn, error)

# CL 132750043 net/http/httputil: Pass a Logger to ReverseProxy, allowing the user to control logging., Mark Theunissen <******@****.***>
pkg net/http/httputil, type ReverseProxy struct, ErrorLog *log.Logger

# CL 148370043 os, syscall: add Unsetenv, Brad Fitzpatrick <******@****.***>