return substring(start, end)
}

/**
 * Returns the index of the first character in this string that contains a character in
 * [delimiters]. Returns endIndex if there is no such character.
 */
fun String.delimiterOffset(
  delimiters: String,
  startIndex: Int = 0,
  endIndex: Int = length,
): Int {
  for (i in startIndex until endIndex) {
    if (this[i] in delimiters) return i
  }
  return endIndex
}

# Custom Response - HTML, Stream, File, others

By default, **FastAPI** will return the responses using `JSONResponse`.

You can override it by returning a `Response` directly as seen in [Return a Response directly](response-directly.md){.internal-link target=_blank}.

      val uri = url.toUri()
      if (uri.host == null) return immutableListOf(Proxy.NO_PROXY)

      // Try each of the ProxySelector choices until one connection succeeds.
      val proxiesOrNull = address.proxySelector.select(uri)
      if (proxiesOrNull.isNullOrEmpty()) return immutableListOf(Proxy.NO_PROXY)

      return proxiesOrNull.toImmutableList()
    }

    connectionUser.proxySelectStart(url)

                return false
            }
        }

        val firSymbol = symbol.firSymbol
        if (firSymbol is FirPropertySymbol && firSymbol.isForeignValue) {
            return false
        }

        return true
    }

    fun getContainingDeclarationByPsi(symbol: KtSymbol): KtDeclarationSymbol? {
        val containingDeclaration = getContainingPsi(symbol) ?: return null

  } finally {
    currentThread.name = oldName
  }
}

/** Returns the Content-Length as reported by the response headers. */
internal fun Response.headersContentLength(): Long {
  return headers["Content-Length"]?.toLongOrDefault(-1L) ?: -1L
}

/** Returns an immutable copy of this. */
internal fun <T> List<T>.toImmutableList(): List<T> {
  return Collections.unmodifiableList(toMutableList())
}

        val expressionCall = binaryExpression.getOrBuildFirSafe<FirQualifiedAccessExpression>(firResolveSession) ?: return null
        val receiverCall = expressionCall.explicitReceiver as? FirQualifiedAccessExpression ?: return null

        return receiverCall.resolvedType
    }

          result.addLenient(fieldName, networkHeaders.value(index))
        }
      }

      return result.build()
    }

    /**
     * Returns true if [fieldName] is an end-to-end HTTP header, as defined by RFC 2616,
     * 13.5.1.
     */
    private fun isEndToEnd(fieldName: String): Boolean {
      return !"Connection".equals(fieldName, ignoreCase = true) &&

        if (this !is KtExpression) return null
        val calleeExpression = deparenthesize(this) ?: return null
        if (calleeExpression is KtCallExpression) return null
        val callExpression = parentOfType<KtCallExpression>() ?: return null
        if (deparenthesize(callExpression.calleeExpression) != calleeExpression) return null
        return callExpression
    }

    /**

          }
        }
      }

    return BasicDerAdapter(
      name = name,
      tagClass = DerHeader.TAG_CLASS_UNIVERSAL,
      tag = 16L,
      codec = codec,
    )
  }

  /** Returns an adapter that decodes as the first of a list of available types. */
  fun choice(vararg choices: DerAdapter<*>): DerAdapter<Pair<DerAdapter<*>, Any?>> {
    return object : DerAdapter<Pair<DerAdapter<*>, Any?>> {

      if (queryNamesAndValues == null) return emptySet()
      val result = LinkedHashSet<String>()
      for (i in 0 until queryNamesAndValues.size step 2) {
        result.add(queryNamesAndValues[i]!!)
      }
      return result.readOnly()
    }

  /**
   * Returns all values for the query parameter `name` ordered by their appearance in this
   * URL. For example this returns `["banana"]` for `queryParameterValue("b")` on