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Chapter 1 - Tutorial

1.2 - Command-Line Arguments

Modify the echo program to also print os.Args[0], the name of the command that invoked it.

Solution

Sample output:
```
$ go run exercise01.go this is a test
/tmp/go-build601632563/b001/exe/exercise01 this is a test
```

Modify the echo program to print the index and value of each of its arguments, one per line.

Sample output:

$ go run exercise02.go this is a test
os.Args[0] = this
os.Args[1] = is
os.Args[2] = a
os.Args[3] = test
this is a test

Experiment to measure the difference in running time between our potentially inefficient versions and the one that uses strings.Join. (Section 1.6 illustrates part of the time package, and Section 11.4 shows how to write benchmark tests for systematic performance evaulation.)

Implemenetations Benchmark program

Sample run:
```
$ go test -bench=. -- $(for ((i = 0; i < 100; ++i)); do echo "arg${i}"; done) | grep -v arg
goos: linux
goarch: amd64
   50000	     24708 ns/op
  200000	      7977 ns/op
PASS
ok  	_/go-programming-language/Chapter01/exercise03	3.167s
```

1.3 - Finding Duplicate Lines

Modify dup2 to print the names of all files in which each duplicated line occurs.

Solution

1.4 - Animated GIFs

Change the Lissajous program's color palette to green on black, for added authenticity. To create the web color #RRGGBB, use color.RGBA{0xRR, 0xGG, 0xBB, 0xff}, where each pair of hexadecimal digits represents the intensity of the reg, green, or blue component of the pixel.

Solution Sample Output
Modify the Lissajous progrm to produce images in multiple colors by adding more values to palette and then displaying them by changing the third argument to SetColorIndex in some interesting way.

In this case, I updated the program to change the foreground color between red, green, and blue on each iteration.

Solution Sample Output

1.5 - Fetching a URL

The function call io.Copy(dst, src) reads from src and writes to dst. Use it instead of ioutil.ReadAll to copy the response body to os.Stdout without requiring a buffer large enough to hold the entire stream. Be sure to check the error result of io.Copy.

Solution
Modify fetch to add the prefix http:// to each argument URL if it is missing. You might want to use strings.HasPrefix.

Solution
Modify fetch to also print the HTTP status code, found in resp.Status.

Solution

1.6 - Fetching URLs Concurrently

Find a web site that produces a large amount of data. Investigate caching by running fetchall twice in succession to see whether the reported time changes much. Do you get the same content each time? Modify fetchall to print its output to a file so it can be examined.
```
With websites that cache generated pages, the second run of `fetchall`
results in faster response times.

The solution here updates `fetchall` to write the responses to files,
indexed by the initial start time and the site's offset into the
argument array.
```

Try fetchall with longer argument lists, such as samples from the top million web sites available at alexa.com. How does the program behave if a web site just doesn't respond? (Section 8.9 describes mechanisms for coping in such cases.)
```
If a web site doesn't respond (i.e., `fetchall` can establish a connection
to the server, but the server doesn't respond with data), then the goroutine
performing that operation will block indefinately, waiting for a response.
```

1.7 - A Web Server

Modify the Lissajous server to read parameter values from the URL. For example, you might arrange it so that a URL like http://localhost:8000/?cycles=20 sets the number of cycles to 20 instead of the default 5. Use the strconv.Atoi function to convert the string parameter into an integer. You can see its documentation with go doc strconv.Atoi.
```
This version makes all of the previously constant values URL parameters,
for example:

http://localhost:8000/?size=300&res=0.002&cycles=10&nframes=16&delay=4

If there's a failure parsing the parameter, the default is used
automatically.
```