CkPython

HTTP Download in Parallel with Simultaneous Range Requests

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Demonstrates how to download a large file with parallel simultaneous requests, where each request downloads a segment (range) of the remote file. CkPython

import sys
import chilkat

success = False

# This requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

http = chilkat.CkHttp()

# First get the size of the file to be downloaded.
url = "https://www.chilkatsoft.com/hamlet.xml"

resp = chilkat.CkHttpResponse()
success = http.HttpNoBody("HEAD",url,resp)
if (success == False):
    print(http.lastErrorText())
    sys.exit()

remoteFileSize = resp.get_ContentLength()

print("Downloading " + str(remoteFileSize) + " bytes...")

# Let's download in 4 chunks.
# (the last chunk will be whatever remains after the 1st 3 equal sized chunks)
chunkSize = remoteFileSize / 4

# The Range header is used to download a range from a resource
# Range: bytes=<range-start>-<range-end>
# or
# Range: bytes=<range-start>-

# We're writing code this way for clarity..
http1 = chilkat.CkHttp()
http2 = chilkat.CkHttp()
http3 = chilkat.CkHttp()
http4 = chilkat.CkHttp()

sbRange = chilkat.CkStringBuilder()
sbRange.SetString("bytes=<range-start>-<range-end>")
numReplaced = sbRange.ReplaceI("<range-start>",0)
numReplaced = sbRange.ReplaceI("<range-end>",chunkSize - 1)
print(sbRange.getAsString())
http1.SetRequestHeader("Range",sbRange.getAsString())

sbRange.SetString("bytes=<range-start>-<range-end>")
numReplaced = sbRange.ReplaceI("<range-start>",chunkSize)
numReplaced = sbRange.ReplaceI("<range-end>",2 * chunkSize - 1)
print(sbRange.getAsString())
http2.SetRequestHeader("Range",sbRange.getAsString())

sbRange.SetString("bytes=<range-start>-<range-end>")
numReplaced = sbRange.ReplaceI("<range-start>",2 * chunkSize)
numReplaced = sbRange.ReplaceI("<range-end>",3 * chunkSize - 1)
print(sbRange.getAsString())
http3.SetRequestHeader("Range",sbRange.getAsString())

sbRange.SetString("bytes=<range-start>-")
numReplaced = sbRange.ReplaceI("<range-start>",3 * chunkSize)
print(sbRange.getAsString())
http4.SetRequestHeader("Range",sbRange.getAsString())

# Start each range download
# task1 is a CkTask
task1 = http1.DownloadAsync(url,"qa_output/chunk1.dat")
task1.Run()

# task2 is a CkTask
task2 = http2.DownloadAsync(url,"qa_output/chunk2.dat")
task2.Run()

# task3 is a CkTask
task3 = http3.DownloadAsync(url,"qa_output/chunk3.dat")
task3.Run()

# task4 is a CkTask
task4 = http4.DownloadAsync(url,"qa_output/chunk4.dat")
task4.Run()

# Wait for the downloads to complete.
numLive = 4
while numLive > 0 :
    numLive = 0
    if (task1.get_Live() == True):
        numLive = numLive + 1

    if (task2.get_Live() == True):
        numLive = numLive + 1

    if (task3.get_Live() == True):
        numLive = numLive + 1

    if (task4.get_Live() == True):
        numLive = numLive + 1

    if (numLive > 0):
        # SleepMs is a convenience method to cause the caller to sleep for N millisec.
        # It does not cause the given task to sleep..
        task1.SleepMs(10)

# All should be downloaded now..
# Examine the result of each Download.
numErrors = 0
if (task1.GetResultBool() == False):
    print(task1.resultErrorText())
    numErrors = numErrors + 1

if (task2.GetResultBool() == False):
    print(task2.resultErrorText())
    numErrors = numErrors + 1

if (task3.GetResultBool() == False):
    print(task3.resultErrorText())
    numErrors = numErrors + 1

if (task4.GetResultBool() == False):
    print(task4.resultErrorText())
    numErrors = numErrors + 1

if (numErrors > 0):

    sys.exit()

# All downloads were successful.
# Compose the file from the parts.
fac = chilkat.CkFileAccess()
success = fac.ReassembleFile("qa_output","chunk","dat","qa_output/hamlet.xml")
if (success == False):
    print(fac.lastErrorText())
else:
    print("Success.")

# Let's download in the regular way, and then compare files..
success = http.Download(url,"qa_output/hamletRegular.xml")

# Compare files.
bSame = fac.FileContentsEqual("qa_output/hamlet.xml","qa_output/hamletRegular.xml")
print("bSame = " + str(bSame))