Form with a "file" type field arrives at the server with "$_POST" empty

Question

On our hosting server, I have two projects, where both are with a module in our administrative area to manage images.

In the project To, the form is submitted to the server and the $_POST is received by the server with the image field loaded.

In the proejcto B, the form is submitted to the server but the matrix of $_POST arrives empty to the server, although in Firebug I can see that the field and the loaded image were sent.

Form

Same for project To and B

<form class="horizontal-form" enctype="multipart/form-data" method="post" action="#">
    <div class="row-fluid">
        <div class="span6">
            <div class="control-group">
                <label class="control-label">Carregar imagem</label>
                <div class="controls">
                    <div class="fileupload fileupload-new" data-provides="fileupload">
                        <div class="input-append">
                            <div class="uneditable-input">
                                <i class="icon-file fileupload-exists"></i>
                                <span class="fileupload-preview"></span>
                            </div>
                            <span class="btn btn-file">
                                <span class="fileupload-new">Selecionar ficheiro</span>
                                <span class="fileupload-exists">alterar</span>
                                <input type="file" class="default" name="img">
                            </span>
                            <a href="#" class="btn fileupload-exists" data-dismiss="fileupload">remover</a>
                        </div>
                    </div>
                    <span class="help-block">Escolha uma imagem para substituir a existente no site.</span>
                </div>
            </div>
        </div>
        <div class="span6">
            <div class="control-group">
                <label class="control-label">Pré-visualizar</label>
                <div class="controls">
                    <div class="thumbnail item" style="width:244px">
                        <a href="http://www.meusite.com/caminho/para/imagem/imagem.jpg" title="Pré-visualização da imagem: imagem.jpg" class="fancybox-button">
                            <div class="zoom">
                                <img src="http://www.meusite.com/caminho/para/imagem/imagem.jpg" alt="" />
                                <div class="zoom-icon"></div>
                            </div>
                        </a>
                        <div class="details">
                            imagem.jpg
                        </div>
                    </div>
                    <span class="help-block">Pré-visualizar imagem existente</span>
                </div>
            </div>
        </div>
    </div>
    <div class="form-actions text-right">
        <button type="submit" class="btn blue"><i class="icon-ok"></i> Guardar alterações</button>
        <a class="btn" href="?mod=website&call=images" title="">cancelar</a>
    </div>
</form>

Information from the Firebug

• Project To

  

  

  

• Project B

  

  

  

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I have already carried out a series of tests to understand what is going on, some of which may be relevant to finding the solution to this problem:

1. PHP file with nothing more than the form above.

   In the project To and B the var_dump($_POST); Give me an empty matrix.

2. Add extra field of type hidden or the type text to the project form B solves the problem and the matrix of $_POST now arriving at the server in condition.

3. Copy PHP file from project To for the project B to check any problems with the file itself (???), but the result is the same.

4. File check .htaccess to locate some directive to Apache, but both files are strictly the same and contains no instructions other than:

   # Use PHP5 AS DEFAULT
   AddHandler application/x-httpd-php5 .php
   
   # Frontpage
   # Set the files to be ignored when ussing the directory list
   
   IndexIgnore .htaccess */.??* *~ *# */HEADER* */README* */_vti*
   IndexIgnore *
   
   
   # BROWERS SERVER FILES VIEW DISABLE
   Options -Indexes
   
   
   # CUSTOM ERROR DOCUMENTS FOR APPACHE REDIRECT
   ErrorDocument 400 /error/400.htm
   ErrorDocument 401 /error/401.htm
   ErrorDocument 403 /error/403.htm
   ErrorDocument 404 /error/404.htm
   ErrorDocument 500 /error/500.htm
   

5. Test on different browsers and different computers to exclude browser or session problems.

   The result was consistent in all tests, project To works well, project B doesn’t work.

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Question

Why does the same form work in the project To, but flaw in the project B and tests with a simple form on both domains fail when you would expect that in the project To worked?

Answer 1

In accordance with the PHP manual the proper way to handle upload in POST methods is using the global variable $_FILES.

// Uma vez que o nome do seu input file é img
$_FILES['img']['tmp_name']

In the OP case, when the form contained only an input file, only the variable $_FILES was fed. Only by including a input Hidden or something like PHP loaded the data representation of this input into the variable $_POST.

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Some other points that may cause problems (not relevant to the OP situation, but that may help other users):

1. The form shall contain the attribute enctype="multipart/form-data"
2. The form shall contain the attribute method="POST" (or PUT, but this is a different mammoth)
3. Make sure you are using double quotes (") in HTML attributes, sometimes you may unintentionally cut and paste smart quotes, angled quotes, etc
4. Check if a Javasscript function is not disabling the input or form
5. Check if your input has a name (attribute name). Just the ID is not enough
6. Make sure that name does not have underscores (_)
7. Check that two inputs do not have the same name
8. Check whether the involved directories have read and write permissions
9. Check whether temporary and destination directories have free disk space
10. Make sure the form is being properly closed </form>
11. Check the settings of php.ini; in particular file_uploads, post_max_size and upload_max_file_size
12. Check the file .htaccess
13. Check whether your source file no problem for chat start, try to upload small files.

Adapted of that answer user’s shamittomar on Stack Overflow in English.